There is a small chance that one of your Common or Uncommon cards can be replaced with a card of a higher rarity
Like most Magic: The Gathering cards, the value of Liberator, Urza's Battlethopter depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (The Brothers' War)
Your win conditions are likely to be either swinging at your opponents with buff Merfolk until their life total hits zero, or you can try to sneakily win using Simic Ascendency , which wins you the game once it hits 20 counters
Prey Upon lets one of your creatures fight anothermeaning they each deal their power to the other
Do some mana fixing by copying Urborg, Tomb of Yawgmoth or commander protection by copying Karakas as long as either of them are in a graveyard
Of course, this runs the risk of your opponents drawing that many cards and still having a main phase, but thats why you have Plagiarize, right