I distinctly recall many speculating, myself included, that Urabrask was the result of the MirariMirari doubly fusing with Slobad's and Bosh's corpses in the Furnace Layer of the reformed New Phyrexian Mirrodin
Because of this, its a popular card, and one that you need a lot of copies of, leading to a high price
Instead, Metamorphosis allows you to tribute a monster, and bring out a Fusion Monster with the same level
Cards that appear on the Multiverse Legends Bonus Sheet do not have their legalities affected outside of Limited play
This card doesnt feature one of the most popular characters in the series, so it pales in comparison to something like Gear Five Luffy from OP05, but Rayleigh is a meta-defining card, meaning itll hold value for a while