Abyssal Templars are level 60 elementals summoned from the Lesser Wind Stones around the various Twilight's Hammer camps in Silithus. The player must wear the Twilight Trappings when interacting with a wind stone to summon one (failure to wear it can lead to shocking results!). The elemental that is summoned is random, but there are items that can force a certain type to appear.
The Abyssal Templars are:
A templar will always drop an Abyssal Crest. Sometimes it will also drop uncommon armor and weapons and trade item relating to the templar's element (such as Elemental Fire from a Crimson Templar). Very occasionally it will drop a rare bind-on-pickup weapon (each templar has its own drop).
A level 60 player can solo a templar but difficulty will vary between classes.