I beat Zilgadis with 11 Green Dragons and 12 Red dragons. If you have the reds, I'm sure you have the greens. (paladin, Impossible, no losses).
However, I had very high physical resist (see famine to feast thread)... and another secret weapon: Zilgadis' first three towers were all evil gremlins. I just let them live because all they could cast on my two stacks was weaken.
I would keep both stacks stone skinned, and use level 1 life light to heal them both at once when it came time to.
You may try to do something similar. Instead of focusing on Ziggy right off, take out any friendly gremlin towers before they can spawn troops, and leaving evil ones. Once he has only evils, go for him. Use plenty of magic resistance and mana spring.
Edit: Sorry, just realized this was for a SINGLE stack. Yeah, you can still do this, but it will be harder without being a mage. The trick will be in not engaging him at melee for as long as possible while you keep his friendly towers dead. I hope you have 95% magic resistance (easy with the gift bag) if you don't.. yeah probably can't be done
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