Common is probably stretching it considering the amount of choices and planning you have to do before even playing this.

Syntax:

> When ~ ETBs, choose one —
> • Untap up to three lands.
> • Until the end of your next turn, target creature can't be blocked.

"You control" clause doesn't seem necessary.
"Unblockable" and "unblockability" aren't (no longer) things in MTG.
IMO putting the duration clause at the beginning is better in this case for clarity reasons.

Mmm, wording is "Target creature cannot be blocked" I think?

But cards that untap lands are mundo dangerous. This is on the less dangerous end of the spectrum, sure, but it's still a potential minefield of balance issues of doom.

­Amphin Pathmage? Note that the card in question has different duration (Commune with Lava).

The fact that this isn't 'free' makes the untapping ability a lot less powerful IMO. It's no Peregrine Drake. It's hardly even comparable. You would need two lands that grant 2 mana to even get "even" with this card mana wise, and three to make any surplus mana - while with Peregrine you are making extra mana with just one of those "tap for 2" in play.

This is only in limited, so the fact that it's in a vacuum means it can't be as easily abused.

Btw, WotC referred to this mechanic in Teferi, Hero of Dominaria where they went with a delayed trigger:

> At the beginning of the next end step, untap two lands.

Maybe it's worth considering? With an end step trigger, I could see it being reasonable for this card to untap up to five lands... I think it would clash badly with flash though.