I'm working on a solo adventure for a paladin PC and I think that magma mephits would be way too effective as their ability to cast heat metal basically means the PC takes 2d8 fire damage every round, no save, until the mephit loses concentration or dies.I'm thinking of replaing heat metal with a fire version of Melf's acid arrow (call it magma blast): ranged spell attack, effectively 6d4 fire damage on a hit, 2d4 fire damage on a miss.
The question is, should I change the magma mephit's CR from 1/2 to 1/4? On the one hand, it is now less effective against PCs wearing medium or heavy metal armor (but more reasonably effective, IMO). On the other hand, Melf's acid arrow is also a damage dealing spell of the same level as heat metal, so it shouldn't change the CR.
What do you think?
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