PavliG
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Here you are, overthinking it :) I simply approached him with 4 stacks of 3 Hellhounds each and won the battle in 2 turns.
However, I couldn't defeat hordes of witches and black dragons near an obelisk, neither on Veteran nor on Hero difficulty, even with a super army of 15 Hellhounds, 700 Manticores, and 700 Thunderbirds in various combinations. There are just too many of them, and even black magic doesn't help.