Recreating spherimorph monster (from FFX) in D&D [closed]

Question

My favorite monster in Final Fantasy X is spherimorph: https://finalfantasy.fandom.com/wiki/Spherimorph#Stats

I would like to recreate a similar monster in D&D 5e.

My starting idea is to give that monster immunity to all kind of damage (fire, cold, acid, poison, lightning, thunder, psychic, force, radiant, necrotic), except one, to which the monster is vulnerable, which changes randomly. In this picture, I suggest the players that only four types of damage are relevant: acid, lightning, fire, cold. Fire is seen (by the monster) as the opposite of cold, acid as the opposite of lightning.

We roll a d4, where: 1 stands for acid, 2 for lightning, 3 for fire and 4 for cold. So if the dice gives 1 the monster became vulnerable to acid, and then it deals lightning damage. Players, seeing that the monster makes lightning damage, then have to target the creature with acid damage. When the creature is hitten and damaged, it randomly (d4) changes its vulnerability.

My creature should have resistance to slashing, piercing and bludgeoning damage, magic or not. I would like to make it immune to several conditions, like prone, grabbed, exhausted, ecc

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I have a lot of doubts about it, it seems to me that this approach is too innatural, making the creature too strong and sham. Not exactly somenthing nice and balanced.

Have you any suggestion? I am still learning how to properly deal with monster creation, so please be polite and constructive, even if my idea is terrible bad for you. Thank you.

EDIT

This monster is intended to be used only within my party, which at the moment are of 8th level. The dice roll to change vulnerability (which counts as an action) is performed in the creature turn. The first turn the creature changes vulnerability, and players that start before the creature can deal to it full damage of every type (namely the creature has not any damage immunity or resistance). I'm still working about fundamental features, but I'm oriented to intend it like an elemental, regarding hit points, damage per round, and AC. The size is large.

I was rightly pointed out that my question is open, and that this doesn't match the policy of the site. I apologize for that, feel free to close if necessary.

Answer 1

This is probably not a monster that will work in D&D as a general thing, because player characters don't really have a way to access most of the elemental damage types without magic, and you can't guarantee your group's casters will pick the right array of options to have all the options needed for this fight. Even if the players are forewarned about the nature of the monster and stock up on acid, alchemist's fire, torches, and so on, you're still pretty likely to have at least one damage type the players can't deal, so you need to have a plan for how to make it switch out of that form -- like maybe have it randomize at the start of its turn if it hasn't randomized yet, I don't know. "The party can't really hurt it this turn" is still a really frustrating thing to hear, it sounds a lot like "go sit in the corner and stop having fun".

But really this isn't going to be very fun even if the team has coverage. If we have two casters who each can hit two of the four random elements, one character who has one elemental attack that might come up, and one character who has no attacks using any of those four elements, on any given round there's probably three players standing around looking at their hands because they can't do anything useful, and one player who is going to have a real bad time with this fight because they just don't ever have something to do.

Furthermore, this is a highly mechanical monster; it's all gimmick and the gimmick is "rub the correct game term against it to continue". In Final Fantasy, that's okay; engaging with the system mechanics is pretty much the entire game experience in-battle, and elementally themed attacks are common even for technically non-magical characters (by using Items if nothing else). But D&D is a role-playing game, and it's much more rewarding to have a fight where the players can be clever rather than just combing through their character sheets to see if they have any way to deal lightning damage.

For example, if this fight were set in a cave full of different elementally energized gemstones that players can throw or sling to cause bursts of elemental damage, but are a limited resource that becomes rarer as the battle wears on, that's starting to provide an interesting tactical fight that doesn't leave anyone out. Still, I'd suggest you want to telegraph what element the monster is aligned to at any given time, because "throw a random element to see if that's what it rolled" is going to be an un-fun combat encounter that sees three out of four attacks wasted to no effect. (Also consider what's going to happen if the players collect the remaining gems to carry them out as weapons for later! I'd suggest they're quartz crystals -- i.e. fairly worthless -- and the elemental charge fades over the course of 24 hours after they're removed from the cave.)

Answer 2

Your group probably won't engage with this in the way you want, unfortunately.

I haven't played Final Fantasy X, but one thing that's true about that series is that one player controls all the characters. So, if you're fighting a monster that one or two characters can't damage, that's fine -- those two characters stand in the back or focus on support, and the rest of the group handles the damage.

That's not true in D&D. In a D&D game, each player controls only one character, and if their character can't contribute effectively to the adventure, that player will be sad and bored.

You might get good results from mixing this monster with "normal" monsters, so that characters that don't have a good damage type still have something to do.

Another thing that appears to be true in FFX is that the party -- through Lulu -- can have access to all the elemental types. That's not true in D&D. A 5e spellcaster might have a cantrip that deals one kind of damage, a spell that deals a different kind of damage, and nothing for the other types. Faced with the monster you describe, the group's reaction probably will be to just hit it with physical attacks despite its resistance.

Answer 3

As it is, this needs a lot more details.

1. When do you roll the d4? At the start of the monster's turn? Then what is it vulnerable to for the first turn of battle, if a player rolls a higher imitative? Would there be any way to determine the vulnerability before the monster's first attack (if not, that feels bad for players as they're punished for rolling good initiative)?
2. What difficulty of encounter do you want this to be? A monster design that works for a high level party might not work for a low level one.
3. Is this intended only to be used in your custom campaign, or do you intend it be a design that other DMs make use of? If so, you must consider how a party without spellcasters would deal with it.

This idea is not unworkable, but you should decide some of these details and create a tentative stat block. Then you can ask a more focused question about the balance.

Answer 4

This needs a lot more fleshing out--ideally, a mockup of a stat block, but at least what offensive actions are available to the monster--but we can address the base mechanic of "multiple immunities, one random vulnerability".

If you have been playing "regular" D&D up until this point (i.e., using the Monster Manual and fielding enemies found in officially-published manuals), this is going to be a very large departure, in terms of pure combat mechanics, from what the players are used to and expecting. At this level, most monsters have 2 damage immunities at most¹ --even incredibly high CR monsters like the CR 30 Aspects of Tiamat and Bahamut have fewer outright damage immunities than are proposed above.

If you field this monster as-is, do not make it a surprise. Arrange for ways in-universe for the characters to know it's out there and research its capabilities so they can specifically prepare for facing it. Getting surprised by one or two damage immunities is rough but doable. Getting surprised by 9 immunities quickly becomes an exercise in frustration as you waste time and resources trying things that will never work. Once you're running the actual fight, you should also figure out ways to make it very clear which damage type is the current weakness, so nobody wastes their one high-level spell slot on an overpowered scorching ray without knowing the vulnerability has swapped to acid.

The players will likely still spend resources and time trying unusual things, but knowing in advance what you'll need to face the blob will help keep the encounter from completely stalling out (and prevent any resulting frustration).

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As-presented, party makeup will make or break this monster in play. A lot of nonmagical weapon-based classes (fighter, rogue, barbarian) will be doing reduced damage or have invested in a magic weapon that is only useful for one round on a random basis (flametongue or frostbrand swords, for example). Caster classes will be wildly swingy depending on subclass, spell, and cantrip choice. Notably, divine smite and a lot of Cleric and Bard damaging spells use damage types not considered in the rotation of vulnerabilities (radiant, necrotic, force, psychic, thunder), and if you go through with the intent to include several condition immunities, that restricts options for support casters even further.

At levels 8 and 9, very few PCs enjoy being told nearly their entire skillset is useless in a fight.

The more the party can prepare for this encounter specifically, the more likely it is to actually work as an encounter, instead of an extended grind of chipping away with swords while waiting for the right type of weakness to pop up.

I agree with Darth Pseudonym, this is an ill fit for D&D. However, if you wish to go forward with it, make sure the party knows the gimmick ahead of time to make it a worthwhile combat instead of a slog.

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^{[1]: I am not counting immunity to nonmagical weapon attacks; to do so would bring this figure to 3.}