RTF is a global modification that replaces all towns in the game.

Damn, I forgot about that. Then it would be better to come up with a different creature and also increase the mages to a normal level.

Maybe it would be better to do this: leave the mages at their current level, and move the messengers/beholders to the third level.

As a creature for the first level, I suggest something like small golems (you can base it on the model of the dwarven defenders, adding something from regular golems). It would be something like short, stone/iron/gold walking armor.