@WolfGirlLover20 Hey! So, meme cave and the crystals they provide are actually from rocks of past planets that had Meme Guardian influence, some of which had rain down on Earth and accumulated into the meme cave mentioned in the Christmas special.
The main intake of Meme Guardians' energy and power is through an old traditional ritual where the spirits of past ancestors of the Meme Guardian race goes into the new generation, granting them their energy and powers. Without the ritual being done, the Meme Guardian can't use any form of power and won't be able to get efficient energy, causing them to slowly die overtime.
And for what sound a Meme Guardian makes, since I did base their design off od cats, they can purr, hiss, and meow like cats do in real life.