Loathe Potion No.9 is the seventeenth episode of Season Three.
Summary
Boomer fears that Mikayla and Boz's budding friendship will blossom into a crush and he'll lose another brother to a Mikayla preoccupation. He gives Boz and Mikayla a Dirt Fairy potion so they'll dislike each other, but the potion is too potent and sends them into mortal combat instead.