Can I use Galarian Slowking's "Mysterious Potion" Ability on a Pokemon that isn't damaged?
Yes, you could try to damage your own Pokemon if you really wanted to.
Mysterious Potion





x2Mysterious Potion
Once during your turn, you may choose 1 of your Pokémon and flip a coin. If heads, heal 90 damage from that Pokémon. If tails, put 3 damage counters on that Pokémon.


Spray FluidCan I use Galarian Slowking's "Mysterious Potion" Ability on a Pokemon that isn't damaged?
Yes, you could try to damage your own Pokemon if you really wanted to.