Would it be balanced to allow Enlarge/Reduce to double its effect when upcast?

Question

The enlarge reduce spell currently has no listed advantage to being upcast. It also seems relatively rare to find 5e mechanics that are able to stack with this spell, allowing you to grow/shrink even more than one size category, but they do exist. I would like to allow slightly easier access to this possibility.

How would the balance of the game be affected if we were to add the following phrase at the bottom of the enlarge reduce spell description:

At Higher Levels: When cast using a spell slot of 7th level or higher, the target grows or shrinks by two size categories instead of one, multiplying/dividing their size in all dimensions by 4 instead of 2, and multiplying/dividing their weight by 64 instead of eight. The damage increase or reduction becomes 2d4 instead of 1d4.

I chose 7th level because it is 5 higher than 2, and I have read that the level 6-9 spells can be considered a separate tier of play to the level 1-5 spells. Thus, in a broad sense, moving a level 2 spell from the lower tier to the higher should result in a level 7 spell slot.

I am hoping that the cost here, a 7th level spell slot, far outweighs the gain of being two size categories larger. The huge weight increase to me seems the most concerning element of this description.

Answer 1

Creature size changes (by two steps) can become problematic

The damage increases aren't the factor that I was most concerned with. What raised my eyebrows was the change of creature size catagory by two opening up mechanics that would never have been possible before.

Levitate

The first thing that came to mind for me is the levitate spell. This spell normally has a weight limit requirement of 500lbs which generally means medium size creatures according to this question.

Allowing a spell to reduce a Huge creature to a Medium may (upon DM approval because weights really aren't defined in 5e), opens them up to levitate as a control option where that normally wouldn't be the case.

There may be other spell mechanics that could be made available as well, but this was the first one I thought of (and it's pretty powerful.)

Grappling

This is another place where PCs normally couldn't engage in a grapple with creatures of the Huge size. There are even builds with races that allow you to act as a larger size that would then enable you to grapple what was once a Gargantuan creature. Grappling is generally underwhelming so I'm not rating this as a major problem, but it does need to be mentioned.

Answer 2

Yes, it would be balanced to allow Enlarge/Reduce to double its effect when upcast.

Tons of spells have no "higher spell slots" effects, so there is no absolutely important need to add such a functionality here. However, since you asked:

+1d4 dg is basically +2.5 dg (on average). +2d4 dg is basically +5 dg (on average).

Combat wise, the first size increase grants Advantage to Str checks and Str saves, plus the extra dg, while your second size increase only gives the extra dg and no more Str.

Can be "reasoned" that at that size all your new extra strength is needed just to hold yourself up, albeit that seems a bit anti-climatic. Exact same logic for Reduce. You just reach some smallness limit, and aren't all that weaker than you look, maybe you'd a bit denser whatever.

Compare with Polymorph, which is "only" a 4th level spell. Polymorph allows one to take the "almost humanoid" shape of a Giant Ape: a huge beast with 23 Str, dealing 7d6+6 dg.

Compare also with Vampiric Touch: Level 3, +3d6 dg, and you heal up half of that!

So, yeah, putting the 2nd size increase of Enlarge / Reduce spell at level 7 is putting it at a way too high spell slot level.

Also, the weight increase can be addressed by supposing that past the first size increase, mass doesn't increase as much, "explaining" that only the extra dg is gained.

Finally, True Polymorph is level 9 and can do way more than just give you Tiny or Gargantuan size. So, an Enlarge / Reduce variant allowing to reach those extreme sizes should be level 8 at most.

So, here is a slightly better balanced version:

Always: Str check and Str saves Advantage (Enlarge) or Disadvantage (Reduce).

Enlarge - Spell Slot level used: 2-4: +1 size, x2 height, x8 mass, +1d4 dg. 5-7: +2 size, x4 height, x32 mass, +2d4 dg. 8-9: +3 size, x8 height, x128 mass, +3d4 dg.

Size increase (and thus height and mass changes) limited to Gargantuan size. However, the dg modifier remains even if so limited (you're just slightly bigger but with clearly more enlarged muscles).

Reduce - Spell Slot level used: 2-4: -1 size, 1/2 height, 1/8 mass, -1d4 dg (minimum 1). 5-7: -2 size, 1/4 height, 1/32 mass, -2d4 dg (minimum 1). 8-9: -3 size, 1/8 height, 1/128 mass, -3d4 dg (minimum 1).

Size decrease (and thus height and mass changes) limited to Tiny size. However, the dg modifier remains even if so limited (you're just slightly smaller but with clearly more reduced muscles).

Weight analysis: Bob the barbarian weighting at 200 lb + 100 of equipment, gets Enlarged.

Large Bob: 2400 lb = about 1 ton. Most structures will have no problem supporting that but wooden floors might creak a bit. Note that if Bob is inside an inn or something, he won't even be "allowed" to Reach Large size at all, growing only enough for his head to touch the ceiling.

Huge Bob: 9600 lb = about 4 tons. Wooden floors will definitely creak loudly, thin ones may even break. Stone structures have zero problem.

Gargantuan Bob: 38400 lb = about 16 tons. Wooden floors break under the weight unless they are quite thick or sturdy, and stone remains ok, unless it is a quite weak stone structure.

Other Ways To Improve Effect With Upcasting

Another way to make a spell work using higher level slots without tweaking the intent and result of the spell too much, is to make higher spell slots affect either duration or number of targets instead.

Edit: In fact after reading comments and a bit of thought, I did not realize how much of a good Reach advantage this could give. Personally, I'd just tell the player: nah, can't do. Tons of other spells don't have up-casting, even if we could find all kinds of ways to turn lots of these spells into up-castable ones, it would just be a big hassle and in the end just give even more versatility, and thus power, to a class that already ends up so powerful it ends up overshadowing almost everybody else. The fact that many sells aren't up-castable is built-in, so, no, end of story.

"Now, if you wanted to do spell reasearch on it to try to improve the exisrting spell, spending months and tons of gold? That's another story."

Then I'd let the player do the "research". I'd probably decide that some other NPC, centuries ago, already tried doing the exact same thing (because it is such an obvious "improvement attempt", and of course since the spell doesn't allow it per RAW, that duce obviously failed. Then I'd determine the odds of the player succeeding himself. Throwing tons more time and money at it would not make the odds better. In the end the player could probably create a completely separate 3rd level spell that allows him to become huge size, and fall to make a generic super-enlarge-super-reduce 1st level spell.

Answer 3

Mechanically I think it's probably fine, if underpowered. But uses of upcasting this spell would probably be in the fuzzy areas of mechanics anyhow.

I may not be envisioning exactly what you intend with this spell upcast as you describe, but I think that overall it would not be game-breaking, nor especially attractive.

The additional 1d4 damage die is pretty underwhelming because a 7th level slot can do a lot more damage than that all on its own. Even if we're enlarging a generic Fighter who can take three attacks each turn, that's a maximum of 12 additional damage per round over 10 rounds for 120 extra damage at most. And that assumes that combat lasts long enough for the Fighter to get ten rounds' worth of attacks. This compares poorly with other spells at that level, such as an upcast Chain Lightning or Circle of Death, which can do quite a bit of damage instantly.

The enlarged creature would already have advantage on Strength checks from the 2nd level casting, so there is no additional advantage there.

Other benefits would be highly situational. For example, some dungeons become easier because areas are easier to reach, or falls less severe. Grappling and shoving become more possible for the enlarged creature to engage in, and harder for others to do to it. Weight is only rarely used in-game.

On the reducing-size side, the effects are similar. The extra 1d4 damage reduction isn't very impressive. The target would already have been disadvantaged on Strength checks from a 2nd level casting. The target becomes more grapple-able and shove-able. For creatures that are already pretty big, reach is reduced and more space is opened around it, which could be helpful.

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The verdict:

It wouldn't break the game by opening up any killer mechanical strategies in general, but the appeal seems very limited to me. It might be great in a scenario specifically designed to require extra enlargement or reduction, but that can be handled by one-off magic items or DM-fiat effects and doesn't apply generally.

I can imagine many story reasons that such an upcasting might be attractive, but the mechanics are less important in cases like that and so balance isn't an issue.