Heart of Kiran What makes the Heart of Kiran so much fun is that you can just pull off a loyalty counter from one of your planeswalkers in order to crew it up
That's pretty saucy from where I am standing, as free dork abuse in the Command Zone can be broken as we know, but here you need to spend six mana, tap it and wait a turn, and then you just don't know what you'll get, if anything, hence it making my second list back here in the Honorable Mentions, but worth it all up and down, and make that choo choo sound
Most commonly, they grant +1/+1 to all your other merfolk, but many do even more, like giving abilities (such as islandwalk or ward), drawing you cards, or making your spells cheaper
But those are just my anecdotes
In FF7, this creates an epic boss battle that can be somewhat difficult depending on how early on you take the fight in the original game, and how prepared you are in Rebirth