Interestingly, the deck's MTG commander Valgavoth, Harrower of Souls doesn't synergize with Great Unclean One at all
However, it's effectively providing a consistent card draw, which is essential for control decks , and if you can get it down on turn one, you can activate the card draw ability on your opponent's turn to have eight cards in hand, then give yourself leeway to play two cards per turn and keep activating it for an additional card draw
No matter, its time to press on
It turns something of an opponents and something of yours into a treasure
I can see this card being really good in decks like Affinity or Amulet, which often use colorless mana but also need specific colors to cast their core cards (like Emry or Arboreal Grazer )
Its a good addition to aggressive decks if you rely on lizard-typal synergies