Preparation There are multiple ways to get to this mob. This is one method, be sure you have digging tools.
Also note that these areas are no-form, so as such you will be unformed. When I did this, Psychosis was enabled in keep which makes this significantly easier as you can all join in on the fight against the mob with only one person "tanking".
This mob is in the soundproof area of keep, which is west side. Take the third west north of southwest corner of keep. Follow path w, sw, s. Then go Down (non-visible room exit). He's down here.
From A Soundproofed Hallway (68286) dig east several times till you hit the dead end. It will teleport you into a long CPK hallway, follow it down and you will eventually find him. A Maggot-Picked Passage (68469) is just outside of his room, and he is aggro.
*Please note: This area is toggleable and can, at times, be NPK or CPK.
Encounter The zombie Trex hits for a decent amount of damage, but is definitely able to be solo'd if you so desire. He has a seemingly random emote that will insta-kill you by biting your head off. Seems to be no rhyme or reason to when this happens and can happen to anyone in combat with him (possibly just in the room?). Other than that, he has no special combat routines, just dispel, spell up with as much as possible and grind it out.
You can flee sw of him to flee into a high-regen NPK room Tunnelling Below the Graveyard Path (68475) to heal up as opposed to other rooms which are CPK.
Loot Generic boss loot
Read Aura
You sense the following: The zombie Tyrannosaurus is a 28 year old, level 500 Skeleton, and is aligned to Death, the Releaser of Life and Ender of All Things. The zombie Tyrannosaurus is immune to: summon charm steal petrification paralysis The zombie Tyrannosaurus is resistant to: magic pierce slash The zombie Tyrannosaurus is vulnerable to: negative mental necromantic The zombie Tyrannosaurus has a Saving against Spells and Most Spell Effects modifier of 14. The zombie Tyrannosaurus has a Saving against Paralysis (i.e., Sleep, Web, Slow, etc.) modifier of 100. The zombie Tyrannosaurus has a Saving against Petrification (i.e., Abjure, Kill, etc.) modifier of 100.Plus Sanc/haste.