You've also got ninjutsu, which lets you swap an unblocked creature with a ninja for a cost, and can be a lot of fun to play with, but mostly in casual formats
If you are looking to invest in a Reserve List card thats going to have a high price tag initially, but I cant conceive will ever drop down, The Abyss is it
Planeswalker decks, or Super-Friends as we usually call them, arent nearly the most popular strategy in Commander
They are the superstar cards of the best of the best decks
It beats out Mortuary Mire strictly because of its swamp typing
While every other FF is represented in the general boosters and the general set of cards, the sprawling nature of Commander Decks means that the four FFs that have a Commander Deck themed around them naturally have a huge advantage - their characters, stories, and worlds are far more heavily represented than the others