An incomplete list that is partially dumb online-specific implementation details and partially state based actions is available at codex_rules/engine.lua at master · sharpobject/codex_rules · GitHub. Here’s a bunch of stuff from that list in English!
- If a player controls 2 Legendary things with the same name, one of them is discarded. Note that if you just play 2 copies of the Legendary thing back to back this won’t happen (the second one will be discarded instead of arriving). You could make it happen if you used Manufactured Truth though.
- Tokens that aren’t in play or in the future are trashed.
- Heroes in the discard go to the command zone and go on cooldown.
- Players with no base lose the game.
- Effects with durations that have expired stop applying (Not actually a state based action, but it’s good to keep in mind that this will happen “fast”)
- If a unit or hero has both +1/+1 and -1/-1 runes, they cancel (This also might not belong in a list of state based actions)
- If a unit or hero just took deathtouch damage or a unit, hero, or building has lethal damage marked on it, it dies. If it was a hero, an opposing hero gets 2 levels. If it was a tech building or addon, that player’s base takes 2 damage.
- Triggered abilities that look for a condition rather than for an event check whether they should trigger, and trigger only if they are not already in the queue. I think this is just Hardened Mox. Way long ago when I wrote this code I said that this also wasn’t really what I’d think about as a “state-based action.”