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whether it was cheating or not, after watching the recording, I think it wasn't (or an Oscar for acting).
what happened specifically in that situation at 123-124 was not Heroes 3 gameplay, and how can you judge that?
1. If they had saved the game as soon as they saw the red hero coming out of the portal and then let the blue player make their last move, if the blue player didn't have "critical scouting" that could have changed the outcome of the game (e.g., Knowledge Spell/Imprisonment), then...
2. And what if the red player hadn't even entered the portal, but had just moved in front of it? Would it be the same, but within the rules? That is, these 100-200 moves (entering the portal) could invalidate the game.
P.S. It's not worth blaming just one person; both players made mutually exclusive "mistakes" (although one is much more significant than the other, but, according to Murphy's Law, such a coincidence happened at that very moment).
Somehow, the mechanics of interrupting the Overlord's Horde (OH) need to be refined, without giving the blue player bonus information, and so that the blue player's move that will be replayed when the OH is interrupted is recorded (to clarify certain nuances in difficult, controversial situations – is this recording necessary?).
And the mechanics should be changed so that after the OH, there is no battle with the opponent for at least one day. But even here, you can cheat, just like with restarting the game upon meeting – not attacking, but only in the case of restarting upon meeting – that's a trick, but with the OH, it's a violation, or something. Perhaps the condition for interrupting the OH should be that the opponent's heroes are in the same zone, regardless of whether it's in the same turn.