I’m honestly the wrong person to ask about that sort of thing, to be honest. I personally try to avoid “off buttons” that just end the game if I can. I’ve always said I prefer to lose a longer, well-fought game of Magic than win by flicking a switch.
One fairly well known one is Mindcrank and Bloodchief Ascension, which I’ve seen at tables occasionally, and another obvious one is the Sanguine Bond and Exquisite Blood combo. These are pretty blatant ones and everybody knows them, but it’s something at least.
I wish I could be more help but it’s not something I go out of my way to find, unfortunately.
Not my expertise, either.