NomadicJoe96, that aspect of Hunting Grounds isn't the real problem, it's more so that it gets you the creature from the hand as opposed to the library. Which means you have to keep drawing tons of cards for it to keep being free value. That would make Kaalia of the Vast go onto this list too, and so the question becomes if that deserves to be here, especially when Elvish Piper would be excluded for needing to have mana paid for each activation.

While Eternal Dominion doesn't specifically require extra mana, the fact that you can't cast spells anymore makes whether or not mana is required irrelevant because of just how huge a payment that really is. (Especially in commander where players are likely to play 3-4 things per turn and you're stuck just getting one.)

Regarding Flamerush Rider, I misread the card and didn't realize it exiled the creatures! Otherwise, Ilharg, the Raze-Boar would be on this list.

I feel like Black Market should go on this list since it spits black mana forever at you for just seeing a creature die. This leads into similar cards like Ashes of the Abhorrent, Grave Betrayal, Moonlit Wake, Revel in Riches, Shadows of the Past, to name a few of my favorites in this vein