I am going to have to get my group to try this as a game variant some time.
The hardest part is keeping track of how many more card plays are owed to each side.
My brother read Wraith's "Stun Bolt" as "That target cannot deal damage until the start of your next turn" instead of "That target has it's damage dealt reduced by 1 until the start of your next turn"; I guess he got it confused with "Throat Jab".
So yeah, I used the card that shuts down the villians deck with Nightmist two or three turns in a a row as well and we completely shut down Grand Warlord Voss' damage and deck on his 2nd side. We proceeded to clean up Voss quite handily. Only afterwards did I start to think "Huh, Stun Bolt seems kinda OP." me not having played Wraith that much.
Botched "Surprise Shopping Trip" from Time Cataclysm in a game where Kismet had "Inconceivable Obstruction" out.
Since I missed "the first time each turn" on Inconceivable Obstruction I got Surprise Shopping Trip triggering a recursive loop of damage and playing more cards which triggered Surprise Shopping trip more - triggering Inconceivable Obstruction again, and so on.
Caught on after I had damaged everything for six or seven points and put another four targets into play in the Environment and was thinking I had stumbled upon something extremely broken.
Scrapped that solo game and started over since I was unclear what the game status was exactly when I allowed things to spin out of control.
The combo will still end up hitting everyone (except maybe Kismet) for a few points of damage and be annoying along with putting a few more Environment cards into play or the trash, but it will not turn into an Environment Deck burner and hero plinking cycle.
That is exactly what it is against the Matriarch, though. *shudders*
We have had a couple, but two come to mind that effected the end of the game.
1) Once, while fighting Voss we believed that Sub-Zero atmospher would negate the effects of Forced Deployment for one turn, as the minions end of turn effects would be moved to the start of the turn, which had already "passed". However, as I now understand it, since forced deployment was destroyed in the start of the turn phase, the start of the turn minion effects would still occur. This allowed us that time to win the game, where we would have lost during that round otherwise.
2) Against Omnitron, we had always interpretted "All Heroes hit for" as being simutaneous, meaning at the exact same time, so when hit by electro-pulse, we would all take the nescessary damage at once. However, reading the clarifications and realizing that we would pick the order we were hit in, we would have very different results, twice. The first time, with Tachyon's Synaptic Interruption I believe the pulse would have been destroyed with her re-direct, sparring my team mates. The second time, both Wraith and Omnitron-X had, "if hit, do 2 return damage" cards, which would have reduced it's HP before it hit our third team mate, Tempest. This would have saved his life, which in turn would have won us the game in that situation, as it was a very close finish.
Anyways, I have read pretty much the entire rule supplement now and hopefully will be able to keep the game changing mistakes to a minimum.