Oversized demons with limited flight ability, able to withstand a lot of punishment.
At 2500 health, Gulaemons are fairly durable, though nowhere near the level of Forest Trolls or Troll Breakers. They also lack offensive power, having no ranged attack and only inflicting a rather modest DPS. Their main trick, however, is the ability to temporarily take flight, allowing them to bypass soldiers and thus skim faster through your defences. Overall though, Gulaemons are not a huge threat, since this ability cannot be used liberally and is disabled near the exit. However, the Gulaemon is abnormally common in later waves of Pit of Fire and Pandaemonium, appearing in clumps of 5 at a time or more. Teslas are thus effective in dealing with them.
Place reinforcements or heroes, or move soldiers in front of towers to make Gulaemons waste their ability in an area with few towers, and land themselves right in the kill zone. To block them, Wraith of the Forest is quite effective. Note that they are still fairly durable with 2500 health, so large numbers could overwhelm your towers. Do not underestimate them.
The name Gulaemon seems to be based on the Spanish word gula, meaning gluttony, one of the Seven Deadly Sins.