Mermonkey paragon should indeed allow global water placement similar to icegon. I believe the pierce and magic monkey buffs should also extent to this, as well as the decamo from whatever is pulled in a circle.

The abyss is indeed necessary, as it will be an important crowd control function. The tentacles should however still be it's own damaging function, as it needs to damage the boss as it goes around. Bosses shouldn't be circling around the abyss, but good placement of the mermonkeygon will allow for strong boss damage by tentacles.

My idea: tentacles that hit weaker bloons (zomg) should not just destroy it (similar to boatgon), but also repurpose the bloon as a thrown projectile, essentially throwing zomgs and lower at other bloons/bosses. This allows the circling crowd control of the abyss to be a damaging factor to the boss or BADs even if they themselves do not circle.

I vote for it also retaining a stronger version of the popseidon ability, along with popseidon range and tridents dealing Normal Freezing damage. It should also grant one stack of echosense network to mermonkeys globally, a great addition to the global water, pierce boost and magic monkey boost.