While working on a character concept around using an opponent's strength against them, I thought of an ability that would make this cool for magic users. Initially, I thought it would be a bard subclass feature, but I don't think I want to make a whole subclass for it. Instead, I made it a feat:
Prerequisite: At least one spell slot
You are practiced at imitating the movements and words of other. Refining your skills you gain the following benefits:
- When a creature that you can see casts a spell of 1st level or higher, you can use your reaction to carefully study their movements and wording. For the next minute, you know the spell and can cast it using your spell slots.
- On your turn, you can cast the spell as normal. Casting the spells in this way still requires all components of the spell unless you have a way to avoid them.
- Your spellcasting ability for this spell is the same as the original caster's. You use your own corresponding ability score to calculate your spellcasting ability modifier.
Once you use this ability, you cannot use it again until you complete a short or long rest.
This feat is basically a watered-down version of the arcane tricksters 17th level Spell Thief ability. It is slightly more available and more interesting though.
Is this feat balanced against other available feats?
Potential problems I've identified:
- Warlocks and clerics teaming up to use the warlock's higher-level slots for healing magic immediately before a short rest.
- Warlocks upcasting other classes' spells. Basically warlocks in general are a concern.
- It makes half-casters even weaker as they have fewer slots to spend on mimic spells.