3v3 just for the ricochet and hitting all abilities is even easier. Mark them, then stun, ult and then jump on them.
Also a lot of these achievements are glitched. Just got 100 kills w/ Nu Wa ult after 1 kill, a lot of these unlock off minions (Rama ult, Sol Ult, Bakasura Butcher Blades, etc), I got Ra healing w/ ~20k healing, and then some won't unlock like Master At Arms, Ouch! and possibly Clay Explosion.