[lauvhk]

I finished an impossible game with no buying strategy as a mage because you get one awesome unit - Sprite - to start with. I only consume those eggs/units containers that are picked up along the road. So no purchase of those items whatsoever. The only items I ever used are Red/Black Dragon eggs and coffins.

The moot point in my game is that I use invisibility which is against your intention. So good luck.

Edit:
1. In my version, you can activate Sleem using the electric charger like you did with Lina.

2. I forgot that I did end up buying Cyclop/Snakes to finished the Magic School rare animal quest so I guess it is not a true "no buying" game. Unless those scrolls are really attractive, you can just pass on the quest.