I never really played MtG, but I love reading about degenerate combos. My favourite uses an unglued (or un- something) card that can remove any card with a silver border you can see from your seat from play. Doesn’t have to be a card in the game you’re playing, other people nearby as valid targets.

The silver border part makes sure it can only be played on other silly un- cards, but there’s a combo with a card allowing to change a colour in an effect to something else, meaning with a bit of support from a few other cards you could technically use this to nuke all cards in all unrelated games around you.