Discussion of level 1 monsters.

Skeletons provide good protection for your archers and mages against enemy archers – it is very beneficial for mages to raise them solely for defense.
Trogolodites are effective against Medusas (surprisingly, their ability prevents Medusas from turning them to stone) – and due to the resilience of Trogolodites, a large number of them can be used to eliminate Medusas, although there is undead, such as skeletons, which also take less damage from Medusa attacks, so skeletons are more useful against Medusas.