First, and most obviously, its Charizard
It can even act as a one-sided board wipe if it has enough counters on it
Card Name Firion, Wild Rose Warrior Mana Cost Type Legendary Creature Human Rebel Warrior Rarity Rare rules Text Equipped creatures you control have haste.Whenever a nontoken Equipment you control enters, create a token that's a copy of it, except it has "This Equipment's equip abilities cost less to activate." Sacrifice that token at the beginning of the next upkeep
Next, you need an opponent with at least seven cards in hand
Thats quite a wide swath of critters, and if your deck is full of solely those creature types, you can even activate this cards Companion benefit
These often appear only in special products like collector boosters, but if you are lucky enough you can find yourself the proud owner of an extremely expensive card