You decide to battle the trainers iddling around the Gym just to get a bit more of experience and money, which you plan to spend on potions.
After a quick run to the Pokemon center (your pokemon need to be perfectly fit, right), you go back to challenge the Gym Leader, who turns out to be no other than ...
Petilil learned Mega Drain
Zubat learned Bite and Wing Attack
Feebas learned Tackle