DELTARUNE's Combat System Is Brilliant

In which the author discusses the combat system of DELTARUNE, outlining how all of the pieces work together to make an engaging whole.

By: TheHans255

6/20/2025

SPOILER WARNING: This article contains spoilers for UNDERTALE as well as for DELTARUNE Chapters 1 and 2, with potential gameplay spoilers for chapters 3 and 4. This article does not contain story spoilers for chapters 3 and 4.

Over the last few weeks, I have had the pleasure of playing the two newest chapters of DELTARUNE, an indie JRPG by Toby Fox. I don't think it's much of a stretch to say that I love this series to death - after all, my avatar for this website is wearing the hat worn by Ralsei, one of the game's main party members. My favorite part of the game is its creative writing and storytelling, though today, in the same vein as my article about Persona's combat system, I want to bring attention to the combat system of DELTARUNE as well, as I find it a fun and engaging part of DELTARUNE's whole and one of several places where it improves on UNDERTALE's very simple but effective combat system.

A Simple But Effective Beginning

Before we can really get in depth with DELTARUNE's combat system, we must of course start with the combat system from its predecessor, UNDERTALE.

If you look purely at what you do on your turn (which encompasses pretty much the entire combat system of most turn-based RPGs), UNDERTALE's combat system is incredibly basic. If you intend on fighting the monsters, you only get a few different weapons and pieces of armor that increase in power over the course of the game, and if you intend to play pacifist (the game's raison d'etre, after all), you don't even get that - all you can really do is perform ACTs to pacify monsters, use the occasional healing ITEM, or even just waste turns as your opponent gives a monologue.

Hence, when designing a combat system for a game like this, one must ask: how does one take a game genre that is normally about using weapons to fight monsters, encourage the player not to use weapons to fight monsters, and still make it fun?

The answer is to take a page from an entirely different genre, the scrolling shoot-em-up (or, more accurately, a variation of that genre called the "bullet hell"), and turn it into the game's enemy phase. Your actions simply involve choosing options from menus, but when the enemy attacks, you will need to navigate a small red heart ("your SOUL, the very culmination of your being") to avoid patterns of bullets and obstacles fired at you. Each monster has their own patterns, and the name of the game is learning to dodge and survive their attacks long enough to spare them (or slay them, as the case may be).

The game begins with mostly straightforward bullet patterns, but extends the system as the game goes on, adding things such as:

• Green bullets that appear in response to certain actions, and must be actively collected in order to spare the monster firing them.
• Blue bullets that will not harm you if you are not moving
• Orange bullets that will not harm you if you are moving
• Alternate "SOUL modes", which change how the SOUL interacts with the bullet board, such as by granting the SOUL the ability to fire bullets of its own

The dialogue trees and such for defeating enemies pacifist can also be puzzles in themselves, especially for boss encounters. Part of the appeal of UNDERTALE is that while you can go through the whole game without killing a single monster, you are always given the option to do so, and that option can be tempting when it is not entirely clear how a monster can be pacified and you don't have the option to run.

While simple, UNDERTALE's combat system is an effective, integral part of its story and world, and remains a versatile part of its gameplay throughout its runtime. It's also robust enough to form the basis of numerous fangames - Undertale Yellow, for instance, uses much the same framework as UNDERTALE with new enemies, dialogue trees, and extra mechanics, including a full alternative to SOUL modes that bosses use to constrict your actions.

DELTARUNE Makes Player Choices More Interesting

So, after the wild success of UNDERTALE, how does DELTARUNE, its successor, expand on UNDERTALE's ideas?

There really is a whole lot I could talk about here, from how DELTARUNE uses personalities and worldbuilding from UNDERTALE in new and interesting ways, to how it tells a compelling story about fantasy and fatalism, to how it puts its characters in grounded, human situations juxtaposed so perfectly with its fantastical ones.

Of course, today we're here for DELTARUNE's combat, and the best way I can sum up how it improves on UNDERTALE is that it utilizes moment-to-moment resource management to make your player choices more interesting (ironically enough, in a game about fatalism). It does this by giving the player a more robust set of actions, splits them among three characters with wildly different abilities, and ties them to a magic resource that encourages risky, adventurous play.

Tension Points Provide a Compelling Short-Term Alternative to Magic Points Or Stamina

Most of Kris, Susie, and Ralsei's more powerful abilities require spending a resource called Tension Points, or TP. TP are spent quite similarly to MP, SP, or PP in more traditional RPGs, where each spell costs a certain amount and can't be used if you don't have enough. The difference, however is in how you get them: while MP or SP typically starts out full per character and is depleted as techniques are used, eventually requiring an inn to replenish, nearly every battle in DELTARUNE begins with your TP set to zero, and you must use actions in battle in order to get TP.

And what are those actions? Well, you might be happy to know that they coincide directly with what might be the two worst aspects of UNDERTALE's combat system:

• In UNDERTALE, you could usually flee from battles, giving you an easy get-out-of-jail-free option for skipping a good chunk of the game. In DELTARUNE, battles are easier to avoid in the overworld, but once you enter a battle, you can no longer run - instead, you are given a DEFEND command that both reduces incoming damage and grants you 16% TP at the cost of your turn.
• In UNDERTALE, there was hardly any incentive to get close to bullets apart from the enemies who use green bullets that must be collected. This is changed in DELTARUNE to where "grazing" bullets - getting close, but not too close - grants TP - at times ludicrous amounts for especially dangerous patterns. (And, of course, it becomes impossible to collect TP if your SOUL has just taken damage and is still in its invinciblity frames).

As will be discussed further in the section about characters, TP gives you access to several essential actions in the game, most notably healing spells (which otherwise requires consumable items or SAVE points) and the Pacify spell that can be used to spare enemies with simpler techniques or by getting them down to low HP. And even if you can avoid those actions, you are still incentivized to collect TP because it will turn into money at the end of the round, which can be used to buy better items, weapons, and armor upgrades.

And, as it should be noted, these actions cost a lot of TP - Susie's Rude Buster attack skill, for instance, consumes half of the bar, while Ralsei's Heal Prayer consumes a third of it. (Oh yeah, and the bar is shared amongst all three characters instead of each character having their own). And since you can't stock TP between fights or build up past 100% of it, building and managing TP is an essential part of long fights.

Kris, Susie, and Ralsei Provide a Versatile RPG Moveset

In UNDERTALE, you played through the whole game as one character, with a relatively basic moveset. In DELTARUNE, however, you play as a party of three characters that each have very different skillsets and roles:

• Kris, the human, is primarily in charge of ACTs, which allow enemies to be spared and/or change their bullet patterns.
• Susie, the monster, has the most HP and the strongest attacks, but also tends to have the most effective ACTs with Kris.
• Ralsei, the Prince From The Dark, is the party's support, possessing both a healing spell and the Pacify spell. He conversely has the lowest HP and weakest attack power of the party.

Most battles have the player carefully manage the strengths and weaknesses of each of these party members and coordinate their actions for the most effective results. The game also has some battles that alter the party dynamic:

• During most of Chapter 1, Susie does not listen to the player and will always choose the FIGHT option to use a melee attack. She also does not participate in most fights for the first two sub-areas, leaving a party of just Kris and Ralsei.
• There are several battles that Kris and Susie each fight alone. During these battles, these characters mostly retain their battle characteristics (including one battle where Susie only chooses FIGHT), but Kris's solo fights also grant some access to TP-costing ACTs that heal or do extra damage.
• During Chapter 2, Susie and Ralsei go on a separate adventure during one section of the game, and Kris is paired with Noelle, a mage character with access to both Ralsei-like magic and damaging ice magic, and can hence be played more like either Ralsei or Susie.
• (There are other changes to the party dynamic, but I'm going to refrain from spoiling chapters 3 and 4 just yet)

Action Order Is Carefully Tuned To Both Enable and Deny Certain Combos

Somewhat counter-intuitively, DELTARUNE does not resolve player commands in the order you choose them. This makes a good deal of sense, since the player always chooses Kris's action first, then Susie's, then Ralsei's, not having the option to reorder them. Because of this, your actions during a turn always resolve in the following set order:

1. DEFEND or using the Tension Bit/Tension Gem/Tension Max ITEMS (Resolves during menu selection and immediately makes the TP available to the characters that follow - cancelling the selection restores the TP back to its previous level and restores the Tension item if used).
2. Kris's ACT selection
3. Susie and Ralsei's S-Action and R-Action
4. SPARE
5. MAGIC (Pacify, healing, and attack magic - note that TP is consumed immediately when selecting these options and is restored if they are cancelled, much like with DEFENDing)
6. ITEMS (except for the Tension items, see above)
7. FIGHT (this is when the quick-time event appears)
8. Enemy phase

This allows you to do a few interesting things:

• ACT with Kris and SPARE with Susie or Ralsei on the same turn - or ACT with S-Action and R-Action and SPARE with another character, including Kris, on the same turn.
• DEFEND with Kris and make TP immediately available for Susie or Ralsei
• DEFENDing with Kris and/or Susie to make TP immediately available for Ralsei. (in particular, defending with both of them gives just enough TP to cast Heal Prayer).
• Use a TP-costing ACT with Kris and immediately build TP back up with Susie or Ralsei, even if you had more than 84% TP at the start of the turn that would otherwise limit the full potential of a DEFEND.

However, there are a few things that you're not able to do:

• SPARE all enemies and use TP to heal on the same turn. Because heal MAGIC always comes after SPARE in the resolution order, and SPARing the last enemy always ends the battle immediately, any MAGIC queued after the final SPARE in a battle will simply never be cast. Worse, this wastes any TP that were spent to select the spell. If you want to heal during a turn, you must endure at least one wave of enemy bullets and risk losing those HP you have just healed.
• DEFENDing with Susie or Ralsei to make TP immediately available for Kris. Any TP that Kris uses for their ACTs must have been available at the start of the turn, requiring at least one enemy phase to have passed.
• DEFENDing with Ralsei to make TP immediately available to Susie. Susie can get TP from Kris DEFENDing, but her spells tend to be more TP-hungry, meaning that her power must also generally be built up from previous turns.
• SPARing an enemy on the same turn that you expect to gain enough MERCY from actions in the enemy phase (such as from touching green bullets).

Also of note is the multitude of Kris's ACTs that require tag teaming with one or both other party members, hence consuming their turns along with Kris's. This provides another layer of resource management - while these ACTs are often more effective at progressing the battle, either for a pacifist or violent result, the characters cannot perform any of their unique actions and are left defenseless, meaning that you must be careful about how those ACTs are deployed. This is especially noticeable if an ACT with Ralsei leaves an enemy TIRED, since Susie does not have Pacify magic and Ralsei must wait until the next turn to cast it.

Knockouts Are Easy Yet Essential To Manage

DELTARUNE's combat system also has an interesting take on when characters are knocked out from their HP being brought below 0. Most RPGs handle this by having knocked out/fainted/dead be its own permanent status condition of sorts that can only be healed with a special item. In DELTARUNE, that special item does exist (the Revive Mint, which cannot be bought anywhere), but instead of setting a status condition, DELTARUNE sets a downed character's HP to a negative number that is half of their current maximum. A quarter of that missing HP is recovered each turn, and when the character goes positive, either from this passive healing or from any active healing (including either healing items or a healing spell), the character is back up again and immediately able to fight. On top of this, the game can still continue with any combination of characters being down and up - it is only when all three characters are downed that the SOUL is destroyed and the game ends.

And this is a good thing, since losing a specific party member can be devastating to your strategy. A tag-team ACT that involves Susie, Ralsei, or both cannot be used if either of those characters is down, and of course ACT itself is locked out if Kris is down. Even if you have the requisite party members for a specific skill, losing the third character can still hurt since they're not around to use items or gather TP.

DELTARUNE's generous revive system is felt all the more acutely for situations in which it's not there. For the battles in which Kris or Susie fight alone, no revive skills are available since the battle ends immediately when their HP hits zero, and there is one battle in the game where the enemy really does knock you down to an impossibly low HP value and disables automatic health regeneration - you'd better have saved those Revive Mints!

Starting With Chapter 2, Mercy is Treated As Its Own Health Bar

UNDERTALE, alongside most of DELTARUNE Chapter 1, has sparability as more of an on/off switch - characters are usually either satiated and ready to be spared, or they are not and still need the right ACT supplied. A few characters have a finite state machine for which ACTs need to be applied, but that's about as far as it goes.

However, a different trend emerges starting with a mid-chapter boss in Chapter 1, and becomes the default starting with Chapter 2: mercy is instead treated as its own percentage-filled bar, shown next to HP in the menu. Each available ACT in the game adds some percentage to this bar, and while there aren't really any build/equipment choices that cause this bar to fill up at different rates than usual, it still requires careful management of your actions in order to get up to 100% efficiently. It's also easy to observe how combined actions change things - for instance, during the fight with the Chapter 2 secret boss, all three characters using their primary ACT adds 7% to the MERCY meter, while individual uses of the ACT only contribute 2%. This overall makes it easy for playing pacifist to have varied, interesting strategies and dialogue trees.

And that leads to one last point:

Sometimes, All You Can Do Is FIGHT

In UNDERTALE, during a normal pacifist playthrough from start to finish, there is only one battle where your attack power matters, and you are discouraged from using your attack anywhere else. While DELTARUNE still has the same ethos of encouraging players to play pacifist, a few of the restrictions are lifted throughout the game:

• First, you (usually) are not actually killing anything when you win most battles by violence, since they run away instead. This does have some effects on gameplay and story, in particular the set of RECRUITS you can add to Castle Town, but most circumstances will not have the game treat you like a monster for defeating things through violence.
• Several bosses (usually mid-chapter minibosses), can only be defeated through a specific sequence of ACTs, and will heal or defend themselves beyond your ability to do damage if you fight too much.
• Some bosses are excluded from RECRUITS, meaning that it matters less outside of their storylines whether you defeat them through violence or not. The secret bosses, in particular, can give either a weapon or an armor depending on whether you beat them pacifist or not.
• And finally, for some bosses, the MERCY meter is crossed out and you are left with FIGHT as your only option. For these bosses, any ACTs that Kris has are usually replaced with other attack and support techniques that can be used instead of actions for filling the MERCY meter.

DELTARUNE's combat system is still far simpler than many other RPG combat systems. There are still only 3 characters, characters do not tend to level up and gain higher base stats apart from getting more HP as the game progresses, there isn't much in the way of status ailments (other than TIRED, anything you do run into is highly specific to a particular fight) and there aren't really buff or debuff skills. What DELTARUNE has, however, is still interesting to play with and is a perfect complement to the story and worldbuilding it presents.

DELTARUNE is owned by Toby Fox, and is available for purchase on Steam, Nintendo Switch, PlayStation 4, Nintendo Switch 2, and PlayStation 5.