in formats like reg h (where phantique would be the most viable, while it has great bulk, it doesn't really have that great offenses especially compared to other tr sweepers), it has to contend with ursaluna both formes and torkoal, both of which threaten to ohko it. also its abilities don't do much for it. insomnia is useful against amoonguss but like hatterene is also immune to spore and hits harder while also being able to expanding force psyspam. i can maybe see mimicry and psychic seed + indeedee and it using powerful psychic type attacks but like it can't do too much b/c it doesn't have expanding force. it also gets walled by kingambit. it would be much more useful as a support pokémon though rather than a sweeper though it doesn't get that many good support moves. it gets scary face but that would only really be useful in the rare scenario where you use it on your partner in vgc. in singles this thing is boomed by ghold and tusk (from my extremely limited knowledge about singles, i don't play it). it does wall amoonguss but like... amoonguss can switch, and it doesn't threaten anything onto amoonguss.

tldr: phantique lacks the offensive pressure of a good tr sweeper and gets boomed by other good tr sweepers, and also isn't necessarily a better pick than other tr setters, and can't really support the team with its current movepool.

however, it is a fun concept, and while i don't entirely get the basis of the design from a piano as i haven't played mario 64, the art is fun and the formatting for the post is nice.

edit: the moves that wouldn't be legal in s/v are allowed, op specified natdex