This one requires two mana and only prevents combat damage, but it justifies its existence with a ferocious effect
Karumonix, the Rat King will have immediate value for rat tribal decks in most non-Standard formats
cascading you can do
Red often requires you to discard as part of the bargain, sometimes giving you card "selection" but not actually card "advantage." Black is the most likely to cost you life and White is just the worst, often having to rely on shutting down an opponent's extra draw in order to get your precious extra cards
I don't think it's ideal because it's super clunky to play around, but it's not particularly expensive and I think can make his value back if you're making good use of the turns where he's extra mana for your pool (pun intended)
Maybe the top end of this is mostly an ego playground for fabulously rich men who'll happily spend $1.77m - the cost of 4.1 million meals for starving people, according to the World Food Programme - on a 2.5 by 3.5 inch rectangle of cardboard, just because they can
