From a competitive standpoint, Tera Grass / Dark is probably the best for it. Meowscarada usually functions as speed control via Choice Scarf on Balance or a Heavy-Duty Boots pivot with Knock Off to remove opposing Boots on Hazard Stack. Since Meowscarada usually runs Protean anyway a defensive Tera is often not necessary. The way Meowscarada is usually played minimizes hits it takes and so minimizes the need for a defensive Tera. Neither is a Tera + Tera Blast needed for coverage because Meowscarada has plenty in Flower Trick, Knock Off, U-Turn, Triple Axel, and Play Rough. Tera Grass / Dark powers up Meowscarada’s STABs, allowing it to revenge-kill more efficiently or harder to swap into. And most of the time there’s something that utilizes Tera better than Meowscarada, so usually it isn’t Terastillized.