Mupy-Mup!
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It's unclear whether the mass phantom and simultaneous summon are a new spell or just a random bug (version 3.1). And regarding the simplicity of the battle – is that a joke? The first seven shots in a row (and mine hadn't even moved yet) take down all the archers and weaker units, so there's no point in continuing.
Added 6 minutes later
I can't open the attachment; could you please upload the save file without archiving it?
It's not a bug; it's a special ability of the Necromancer – at the beginning of his turn, he creates phantom archers. And summoning elementals is just his own initiative.
This is a really easy and boring battle.
The replay is attached; there's no archive.