This is an old mechanic from a time where creature combat wasnt such a huge part of MTG like it is today
Every other timing rule for casting spells still applies: If the mayhem card is an instant, you can cast it any time you have priority that turn, but if it's a creature you can only cast it at sorcery speed (unless another effect gives it flash)
This cards interesting, moody art (I love the yellowish flower atop Venusaurs back thats normally pink) and supreme scarcity mean that finding a good-quality copy of this card is quite difficult, let alone a highly-graded one
We selected the Mewtwo GX (Secret Rare) from Shining Legends because Mitsuhiro Aritas laboratory illustration is the most narratively significant piece of the Sun & Moon era
For foiling we have seen non-foil, foil on one side, and foil on both sides as well as different foil variations
Return three snow lands you control to their owners hand: Return this creature to its owners hand