Gremlins

I almost agree...

Added 20 minutes later
and about the Gremlins...
1. The pests won't be able to defend the city... they are useless against a hero-artilleryman (fully upgraded catapult). The catapult goes first and destroys half of the fortifications + you can choose a target (for example, the gate) and + with the "Engineer's Ring," the walls are completely destroyed. Moreover, a lot of Gremlins are needed for the ability to work.
2. Gremlins are useful in a team with machines (or against them)... like many others, they become a force in a team with appropriate units.
3. Sorry, but I don't really like mages (I don't play as them much).
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*Gremlin-sadists (modified pests) were really an overpowered and scary force.
*Lizardmen from the Depths (modified lava dragons) could destroy everything in their path (including walls).