The card then tells you what happens if the kicker cost is paid
You get to tap your rocks for mana, bounce them back to hand, and then recast them to increase your storm count and hopefully even net extra mana, although that requires more artifacts that produce more mana than they cost like Sol Ring, Mana Vault, and Grim Monolith
It is a bit unusual in that its evolved form, Urshifu, has appeared on a total of 8 different cards
You can find the full list of legendary creatures, and this also includes the all-powerful monkey Ragavan, over at the Multiverse Legends card gallery
If youre using this ability on your turn, youll create more creatures to sacrifice to the ability, making this card somewhat self-sustaining
Also, since the Burning Abyss monsters have their effects activate in the GY, youll have the advantage with cards whose effects activate in the GY when you send monsters you control from the field and hand to the GY