Other Abilities include the AD&D Spells:
Command, Comprehend Languages, Detect Alignment, Gate, Geas, Quest, Teleport, True Seeing
All these are natural abilities and are not subject to the magic rules of Guyendor.

 

Background

Tiamat represents the acceptable evil in the world. Even priests of Bahamat, whilst reviled by Tiamat and her order, accept that she is necessary. At the end of the Valheru wars, Tiamat became the Guardian of the Hells and Abyss. It is commonly held that she probably is the only entity between the Devils and Guyendor, if Tiamat were to 'disappear' then these evil creatures would return to follow Set in the destruction of the world.

All this is not to say that Tiamat is not cruel. Until quite recently many of her temples were hidden due to unpopularity. (Probably because of the human sacrifices that were part of her rituals). This has changed, however, and in some cities of the empire Tiamat is now openly worshipped (the more bloody rituals are very rarely practiced).

Appearance
Tiamat resembles a 5 headed hydra, with one head representing the most common of the chromatic dragons (red, blue, green, white & black). Her body is grey and she supports huge wings that come from her shoulders.

Combat
Tiamat has many strategies when in combat. She can create very detailed illusions (-8 on saving throws) which she uses to lure and evetually kill those unfortunates. 
She has unlimited breath weapons from all five heads.
If Tiamat prefers (quite rare) her physical attacks include five bite attacks followed by a tail.
Finally any mortal touching her skin must save vs poison or die a slow agonising death over the next 6-12 hours (1d6+6).
She is a formidable opponent who few could beat in open combat.