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Yes, in theory, but he can also slow down units. Let's say he's waiting; we cast teleport. After that, he will definitely have a turn with the Hydras because the Bone Dragons will move later due to the waiting mechanic, and he can either slow them down or speed up his entire army and block the gates. So, it might work, but compared to the speed-boosted Archdevils, it still feels off. Archdevils essentially get the last turn of round 1 and the first turn of round 2. So, if there are no speed boosts or slows in round 1, you can cast a prayer or blessing, or anything else, on them, and they will fly out, attack, and fly back guaranteed. In short, it's much more reliable compared to Hydras. That's why I'm saying I don't even have any fantastic, let alone reliable, ideas. I understand your idea, but it's unclear where the skeletons will be and whether they will reach their target. If they reach it the first time, he will simply remove them the second time.
P.S. You could simply use native magic and a good mage hero and shoot Implosion at him while the wall holds. But there's no guarantee you'll get native magic; you might capture it, or you might not. In theory, everything is possible, but there are too many random factors.
P.S.2 Maybe he's just an inconvenient opponent, and that's all