How ripe for abuse is a homebrew spell that modifies the weight of an object?

Question

I'm working on a custom class and trying to come up with some novel things they might be able to do by writing magical glyphs and runes on objects.

I was thinking an interesting effect might be one that simply makes an object that a glyph is drawn on weigh an additional 50lbs. The limitations on the spell would be:

• Object must have at least 6 square inches of contiguous surface area (So doing it on chainmail, really small coins, or grains of sand would be impossible).
• No restrictions on whether or not the item is worn or carried. Could still be cast on an enemies shield, etc. This would allow for the enemy to make a dex save to prevent the effect.
• No weight restriction on the item it's cast on, doesn't matter if it's a piece of paper or an anvil.
• Has resource consumption via spell slots.
• Requires an action to cast, and has a range of Touch.
• Is granted by the class at 7th level.
• Should be roughly equivalent to a 3rd level spell in power.
• Lasts an hour. This might increase if upcast with a higher level slot.
• Only one active at a time - drawing this rune again causes the previous to disappear.

Now, the last one there might have some weird physics-puzzle implications, but that's fine by me.

Would a spell like this potentially break anything? I can't find any other weight-modifying spells that function similar to this, but if you are aware of one that is useful to compare, that would be great.

Answer 1

Hmmm. Sounds like "Telekinesis, Straight Down Only".

Whenever you create a new power or spell, look for things that already exist that are similar. This seems a lot like a Mage Hand, but with the 10 pound limit raised to 50 pounds and the limitation, "Only to send things towards the floor". Mage Hand has a duration of 1 minute, does not require Concentration, and is more plainly visible than your spell.

Overall, it seems like this spell is in the same general class as Mage Hand. It would not be outrageous to consider it a cantrip (as long as you keep the one-at-a-time limitation). Personally, I tend to be conservative with my home-brew stuff and would err on calling it a 1st-level slot. (You can always change your mind later.)

To get a 3rd-level slot-worthy power, I think you could up the weight to 500 lbs. I would establish up front how much damage a 500 lb feather does upon impact - it should be substantial, considering what other options a caster has for a third level slot.

Answer 2

On the face of it it seems remarkably underpowered.

Unless playing with the variant encumbrance rule, the weight of an object is completely irrelevant. Sure, it could turn something like a wooden spoon into a usable improvised weapon but, seriously, how often is that going to be your only available weapon choice?

One way to judge a spell's power is to put it next to others of the same level and ask "Would I always/never choose it ahead of those?" If it was a third level spell, is it is clearly inferior to many other choices on every class' list. This is an underpowered spell.

Add to the fact that it takes up your 7th level boon and my reaction to this class is "no, thank you."

Answer 3

I accepted an answer, but I thought I'd also answer my own question in order to draw out some of the thoughts posted in the comments.

This spell is not so much directly ripe for abuse, even with a higher set weight, which would probably be necessary to make it roughly 3rd level. What it actually is, is a pain in the patootie to rule on as DM, or make rules on as the homebrew author.

Here are a couple of the potential uses for the spell, some mentioned by users in the comments:

• Carrying an object up to a high point, making it really heavy with the spell, and then dropping it on an enemy.
• Casting it on an opponent's armor or shield, in order to force them to drop it, or disable them.
• Using it to make a melee weapon more deadly, even if more cumbersome.
• Lowering your center of gravity to make it more difficult for you to be knocked over, or giving yourself more weight to slam into other people when taking the Shove action.

Those things present some problems:

• How do you calculate the damage of a falling object if it collides with somebody? A terminal velocity brick weighing (potentially) hundreds of pounds should do some substantial damage. Even worse, how do you calculate the hit chance? The higher the fall, the more substantial the damage, but also the further away the target.
• An overencumbered enemy is easy pickings, even if they're simply prone. If their breastplate is suddenly is so heavy they cannot stand, are they simply restrained? What do they have to do to break the effect?
• How much more damage should a heavier weapon do, and how much more difficult should it be to swing?
• How much should this affect the Shove action?

Now, a creative DM can come up with fun consequences for any of these things, which is great. However, part of the appeal of spells is that they have a very specific, written way of affecting the rules and changing the game world.

DnD 5e isn't GURPS - you won't have various charts explaining how to make your die rolls simulate physics. Therefore, the homebrew would need to either address the problems above directly by providing such rules, or leav them to DM fiat. Providing rules quickly turns 5e into a more simulationist style that bogs down play and could cause other issues down the road with player expectations, and leaving them for the DM makes the spell much less reliably useful, as well as much less appealing for any prospective DM to allow.

So the answer to the written question is no, it doesn't directly break the game, because the consequences of such a spell are largely unwritten, so it'd depend on the DM. The answer to the unwritten question "Would this be a good homebrew spell for 5e?" is also probably no, since the physics consequences become complicated very quickly, and 5e doesn't help much for resolving them.