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)
There is a small chance that one of your Common or Uncommon cards can be replaced with a card of a higher rarity
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
Return that card to the battlefield under its owner's control at the beginning of that player's next end step
You either create cards that just objectively suck (i.e.: most of this list), or you risk making an actual good leyline that breaks the game by nature of how these cards work
Popular sets include Scarlet & Violet, Crown Zenith, and 151