An opponent can use artifact removal on it and destroy any creatures granted islandwalk by its effect at the same time
Unlike green, most colors have trouble ramping by searching for lands, and this perfectly fits that bill and even sprinkles a little card draw on top
For as long as it remains exiled, you may play it, and mana of any type can be spent to cast that spell
And this is by no means definitive, since I have not played every video game ever to have discovered every Magic nod
Goblin Cratermaker is flexible since by paying and sacrificing it, it can either remove small creatures or eldrazi titans target colorless nonland permanents (like artifacts)
My Predictions on the Main Commanders I predicted that the main commanders would have two of their colors represented in their casting cost and the other two in their activated abilities