You can Return this card into the Extra Deck, then Special Summon 2 "Paintbrush Artist" monsters from your Deck
It gets around indestructible effects, and can even return Extra Deck Monsters to there in order to make the resources that went into them useless
What makes this red creature so good is that you get to deal damage to any target based on the power of your creatures that enter play, and you can use it to control the board or just combo-kill your opponent faster
Petrahydrox's ability resolves before the spell or ability that caused it to trigger
It has quite a bit of flaws, most notably requiring the right setup and attribute limitations to maximizing it out, but a properly timed Mithra wins games
Obviously we couldnt talk about everything in just 20 cards, so if theres something we missed, why not let us know on X