However Rotpriests ability doesnt care who targets your creatures, allowing you to fire off multiple, cheap spells and win the game
Then there are a few others that call for some creative and/or more narrow applications
Whenever you discard a card, target creature an opponent controls gets -X/-0 until your next turn, where X is the number of different mana values among cards in your graveyard
Snek Any card depicting a snake, thanks to the meme
Itll give you clues for creatures leaving, sure, but also if your Ozolith gets blown up, or a Planeswalker is retired
In general terms, companions encourage creative deckbuilding and reinforce the idea that self-imposed restrictions can be fun and novel