I wasn't sure where to post this, but since it's fun, fan-made and unofficial, it seemed most appropriate here.
So, the existing four-player rules still leave something to be desired IMHO: there is relatively little interaction between team-mates and battlefields, so that it still only feels like "parallel play."
Here are the house rules I've put into effect - while their differences from the standard four-player rules are subtle, they address the major problems fairly well, and make four-player games as interesting as I feel they should be.
Please post your feedback, questions, & suggestions here, and try a game with these rules first - see if you don't like it better than the standard four-player rules.
Four-PlayerSummoner Wars: House Rules (1.1β) [PDF]
Players 1 & 3 are allies against Players 2 & 4. The highest roller determines which player goes first (ie. who will be “Player 1”), and standard first-turn rules apply. Turns go 1-2-3-4, repeating (see image).
1. a) Allies share one communal Magic pile and one communal discard pile.b) “Your side of the Battlefield” refers to your team's collective half of the gameplay area.
2. Units may move and attack freely between the two Battlefields as if the inner buffer between the game boards did not exist. The outer edges of the Battlefield are absolute.
3. During your turn, your ally's Walls are considered “under your control” – you may summon to spaces adjacent to them, and Events/abilities that affect/employ Walls which “you control” extend to your ally's Walls as well.
4. During your turn, you may not Move or Attack with your ally's Units, but Events/abilities that affect/employ Units which “you control” extend to your ally's Units as well (eg. The Demagogue may mutate his ally's common Units).
5. Events which stay in effect “for the duration of your turn” will remain in effect for the duration of your ally's turn as well. Events which are in effect during an opponent's turn remain in effect for the duration of both opponents' turns. Multiple Events in play remain active simultaneously (“stacking”).
6. When your Summoner is Destroyed:
- Your Summoner goes to the Magic pile of the player who destroyed it.
- All of your faction's Units and active Events are discarded; however, your Walls remain in play.
- Any enemy Units under your influence (eg. “Mind Control”) return to the control of their original Summoner; if the original Summoner of a given Unit has already been destroyed, that Unit is discarded.
- Your Draw pile and hand are discarded; your team's Magic / discard piles are otherwise unaffected.
- You are skipped in the turn order for the remainder of the game (ie. the surviving player doesn't get double-turns).
Games where one player is responsible for two Summoners follow all of the above rules, but with the following exceptions:
- The turn-order is 1-2-3 repeating, where “Players 1 & 2” are always allys against the combined forces of “Player 3”.
- During the first round, “Player 1” skips his turn entirely, but “Player 2” takes his turn normally.
- “Player 3” draws from one combined deck, instead of two separate ones.
- On each turn, “Player 3” begins with ten cards, may move up to six units up to two spaces each, and may attack with up to six Units.