You need colorless mana (of course) to activate the ability, and your creature comes back tapped, but its certainly a valid option
The joke here is that Neriv makes mobilize tokens hit harder, but thats true of any creature that can come in attacking immediately
Duskmourn: House of Horror - a strong pick if you like horror flavour, tense Limited games and a set that feels very different from normal fantasy Magic
You do then lose the bonus from having the transformed version on the battlefield, but it can still be good to get a second ETB
Gyarados exs attack, Rampaging Whirlpool, dishes out 140 damage while also letting you choose a Pokemon on the field to discard an Energy from
Floodgate Trap Hole MP17-EN114 YuGiOh 2017 Mega-Tin Mega Pack Keep track of your collection value over time