For a lot of loops, the key is being able to remove things from play, such as with Mandarin or Bonfire, so that they can be played again.
Yeah! Unless I’m mistaken, the only two voluntary acts a player can do for herself, without specific command from cards or situation, are “play” and “buy”. These two acts are the driving force of the game. So maybe the loop enablers in a strict sense are just the cards which establish a game state in which infinite plays or infinite buys are possible.
I will try to list the features of infinite-loop enablers and the cards that have these features. I think these are the features that make possible infinite plays or infinite buys of the same copy of a card. If it’s right, we wouldn’t be able to make an infinite loop without one of these cards.
I'm not sure if the list is complete, please tell me if I forgot some card with a certain feature or some other feature that enables infinite plays or buys.
Cards that return phasesVilla
Cavalry
Cards that allow play actions in buy phaseCapitalism
Gamble
Toil
March
Scepter
Cards that remove cards from playMint
Horn of Plenty
Mandarin
Urchin
Pillage
Procession
Death Cart
Counterfeit
Madman
Spoils
Raze
Bonfire
Engineer
Small Castle
Pixie
Wish
Acting Troupe
Magic Lamp
Experiment
Stockpile
Horse
Way of the Butterfly
Way of the Horse
Obs:
- Cards that go to Tavern Mat remove themselves from play, but only when played, not when called, so they can’t be played repeatedly
- Knights can be removed from play, but it depends on the opponent deck
- Encampment also can leaves play area, but returns to the game only in clean-up phase
- Monastery, Changeling, Vampire and Bat remove cards from play, but only in the night phase
- Improve remove cards from play, but already in the clean-up phase
Cards that remove cards from the trashLurker
Fortress
Graverobber
Rogue
Treasurer
Cards that return cards to pileAmbassador
Madman
Spoils
Wish
Experiment
Horse
Way of the Butterfly
Way of the Horse
Obs: Encampment also do it, but only in clean-up phase
Cards that make at least one action play that doesn’t put a card in play area Throne Room
King’s Court
Procession
Band of Misfits
Disciple
Inheritance (Inherited Estates do it)
Overlord
Crown
Scepter
Citadel
Captain
Way of the Mouse
Obs:
- Innovation can do it, but only once per turn
- Royal Carriage can do it, but only once per turn for each copy of it
- Necromancer can do it, but only once per turn for each card in the trash
- Mastermind and Ghost do it, but only in your next turn
Cards that make at least one treasure play that doesn’t put a card in play area Counterfeit
Crown
Cards that can be bought repeatedlyForum
Scouting Party
Travelling Fair
Delve
Gamble
Pursue
Toil