There are a ton of different items and ways to store your MTG cards
Similarly, if you sacrifice a creature to activate a mana ability while activating Heirloom Epic's ability, that creature won't be on the battlefield when you pay the ability's activation cost, so you won't be able to tap that creature rather than pay one of the mana in the activation cost

Doomsday: Out: 1x Shattering Spree, 1x Damping Sphere, 2x Fable of the Mirror-Breaker In: 2x Grafdiggers Cage, 2x Unlicensed Hearse Bazaar Decks: Out: 3x Maddening Hex, 1x Trinisphere, 1x Shattering Spree, 3x Damping Sphere, 1x Chalice of the Void, 1x Pyroblast In: 2x Alpine Moon, 3x Fury, 2x Grafdiggers Cage, 1x Pithing Needle, 2x Unlicensed Hearse Additionally, if you suspect they have Collector Ouphe: Out: 2x Pyroblast In: 2x Dead // Gone Oath of Druids: Out: 3x Damping Sphere, 1x Shattering Spree, 2x Fable of the Mirror-Breaker, 1x Legion Warboss In: 2x Alpine Moon, 2x Dead // Gone, 2x Grafdiggers Cage, 1x Pithing Needle Creature-Based (Humans, etc.): Out: 3x Pyroblast, 3x Maddening Hex In: 2x Dead 3x Fury, 1x Pithing Needle If you dont think the opponent has good activated effects, like if theyre Mono W Humans without Cathar Commando, you can board in Unlicensed Hearse instead of Pithing Needle

Whether youre building around Sauron, the Dark Lord in a powerful combo list or sleeving it up for a casual pod, having access to this card at a fraction of the original price opens up your entire deckbuilding strategy
The Golden Chocobo is the endgame of the Final Fantasy VII breeding quest, so it makes sense to see it represented on such a rare card here
For this reason, its a pretty useful card to have in duels, if you have five ink to play it, of course