In a go-wide deck it'll be particularly effective, since blocking a 1/1 token and paying mana or taking extra damage feels like a terrible deal
The Earthen Ally is a humble 0/2 for one Green mana, gaining power for each color among Allies you control
Featuring the unnamed gating mechanic that forced you to return a permanent of the same color to your hand upon entering, that so-called drawback didn't hurt the Wurm's playability, as getting back a Blastoderm that was about to die from fading or returning a Thornscape Battlemage to reuse its kicker abilities was nothing but a benefit
The downside with these Planeswalkers is that they cannot draw you cards immediately like Garruk, Primal Hunter can as they require quite a bit more loyalty to use their card draw abilities than what they start with
Registration Errors: As the name would suggest, registration errors occur when one or more of the color passes ars not correctly aligned
Its the kind of complexity you expect from a Modern Horizons 2 Mythic