"Its circular mouth is lined with rasping teeth. If its prey is hit by both clawed tentacles (1d4 hp damage each), it is drawn up against this orifice for an automatic 1d6 hp damage per round of contact. This mouth can rasp through armor at a rate equal in rounds to the difference between the AC and 10. For example, chain mail (AC 5) requires 5 rounds before actual damage to the victim results, while plate mail (AC 3) requires 7 rounds. If the victim breaks away before it takes any personal injury, damage to the armor still takes place."
Rend Armor (Ex): If a tyrannabyss hits with both claw attacks, it pulls apart any armor worn by its foe. This attack deals (4d6+18) points of damage to the opponent?s armor. Creatures not wearing armor are unaffected by this special attack. Armor reduced to 0 hit points is destroyed. Damaged armor may be repaired with a successful Craft (armorsmithing) check.
I think the rend armor attack is close, but not quite on. For the bebilith, you have a creature ripping apart armor (not damaging the character), but here, you have a sawing mouth that grinds through the armor to get at the character underneath. Therefore, we probably need an improved grab combo, with the rend armor. If no armor is worn, or the armor is destroyed, then the character takes the bite damage instead.
As for fast healing, I'm not going to worry about it saying any old stupid 1 hp per turn, and assume that mean a round instead.
Fast Healing (Ex): A tyrannabyss heals only if it is submerged in seawater.
"Below the mouth of the tyrannabyss is its primary hunting weapon, an elongating tube that can fire a barbed sting to a range of 10'. Its sting paralyzes (saving throw applicable) its prey and the tube is retracted to draw its victim within range of its tentacles. If the saving throw is made, victims with a strength of 15 or better can resist the pulling tube, but take 1 hp damage per round due to the lacerations from the barbed sting. The sting can only be used once; then, 3 turns are required for it to be rearmed."
For the moment, I'm not going to worry about how long it takes to reload. We can resolve that later. For starters, I looked at an old 3.0 conversion here on ENworld (done by Southern Oracle, who still posts from time to time):
http://66.34.111.89/Eric/conversions/tyrannabyss.rtf and found something that we can hopefully adapt:
SA -- stinger: The stinger can be fired a maximum of 15 feet and has a range increment of 5 feet. It causes 1d4+3 damage and delivers a paralytic poison. The tyrannabyss takes 3 rounds to retract the stinger, allowing an opposed Str check each round to break free. Anyone breaking free suffers an additional 1 damage from the barb tearing free. When completely reeled in, a victim is subject to automatic bite attacks. The stinger tentacle has AC 14 and can take 8 points of slashing damage before being severed.
SA -- paralysis (ex): Anyone struck by the stinger must make a successful Fortitude save (DC 16) or be paralyzed for 2d6 rounds.
"It has the ability to assume the coloration of its surroundings and its boneless body can squeeze through openings considerably smaller than its body size. It cannot squeeze under doors or through small cracks. If a man can crawl through an opening, so can a tyrannabyss."
And from the same conversion:
SQ -- camouflage (ex): This grants the tyrannabyss a +4 circumstance bonus to Hide checks.
SQ -- contraction (ex): The tyrannabyss has no bones or solid organs and is able to squeeze itself through openings much smaller than its apparent size. As a general rule, if a Medium-size or larger creature is able to fit through an opening, so is the tyrannabyss.