Matoya wont win a game on its own, but it finds the pieces to do so
Im sort of afraid to ask what you think, but I can be tough
If this thing was a named legendary creature - even if it was a new version of that weird little rat Loot - it might feel like a mythic rare, purely on the basis that "cute little guys" is an established archetype for extremely rare and powerful creatures
On the other hand, Vampires are an extremely popular and well-represented creature type, which also means it is pretty difficult to shake things up
cEDH Decks An common way to do this is to create an infinite mana combo for mana through cards like Isochron Scepter and Dramatic Reversal paired with some mana rocks
Royal Assassin becomes even more powerful when you introduce ways to tap your opponent's creatures, like Orb of Dreams, making it always viable