Heroes of Might and Magic IV is a turn-based strategy game developed by Gus Smedstad through New World Computing and published by the 3DO Company for Microsoft Windows-based personal computers in 2002. Exploring Heroes 4 game to its limits, there is a summoning tree that give unique units, but require a combination of two magic trees.
To cast the Summon Ice Demon spell, the hero need Expert Nature Magic and Expert Demonology. So the hero must have nature and death magic at the same time. Ice demons are medium speed army, quite versatile and have a chance to freeze the enemy, which makes them useful even in small numbers.
At first levels of Demonologist and Nature magic we can Summon Skeletons. Second level allow summoning Imps, they are week but flying and steal mana. Next level bring the Cerberus, fast and hit up to 3 targets. And finally the Ice Demon.