Playing as the Legions (Disciples 2).

I usually took a warrior hero and leveled him up as a fighter. I placed an Incubus in the back and two Berserkers in the front. Sometimes I leveled up a Demon, but not into a Tiamat, but into its neighbor with the burning attack. I often used and leveled up a Gargoyle; if it wasn't killed early on, it would level up easily later. It's large, of course, but it starts with armor and two of its upgrades seem to increase its defense to 60. Also, as it levels up, its defense, HP, and damage increase, and its attack is "Earth," which pierces and effectively damages undead creatures with physical damage immunity. It's best to give it to a mage hero so that he can hide behind it and level up more freely. I never took any dragons for myself – it's too questionable of a choice for the cost. You can, of course, replace the Incubus and fire-based units with a copier, but the Incubus is the best choice without a doubt.