Well, there are 4 types of Gremlins:
Gremlin Deciever (lvl. 5 controller)
Gr. Skulker (lvl. 7 lurker)
Gr. Conniver (Lvl. 17 controller)
Gr. Prankster (lvl, 17 minion controller)
There "racial" abilities are an aura that gives all enemies a hefty penalty to skill checks and the ability to swap places with an adjacent enemy who misses it with a melee attack.
The Deciever and Conniver have charm powers, while the skulker has a very potent stealth ability, at least until the PCs figure out how it works.
Fluff wise, they like to cause mischief which is blamed on others. Deciever steals stuff, and then plants it on others. The Skulker is essentially a serial killer. The Conniver works by miscommunication, getting others to mistrust and war with each other.