Is it possible to make a macro that casts Mutilate above 35% and Backstab below?
No. Macros can’t make decisions based on health. Q: But what it I… A: Still no. Some people sort of fake this by keeping two bars – one with Mutilate and one with Backstab – and manually switching between them at 35%, but the key word there is “manually”. I also think its a bad idea in general, as you will sometimes need to throw some Mutilates even below 35%, so having both keys available to you strikes me as generally a positive thing.