I'm not sure if the Diadron looks more like some weird melty-guy humping an inflated stomach or some poor unfortunate sweaty-guy with massively swollen gonads to me.
That's exactly what the Diadron is - a hideously deformed mutant
You see, I wanted to come up with something original, as most of the floating monsters are just Cacodemon-clones. Besides, there aren't any demons in Tristania 2. Here is what the Tristania 2 booklet has to say:Class: Unknown
Firepower: Light, heavy, very heavy
Probably the most disgusting abomination brought to life by the Courbée Dominate, and also one of the most fearful creatures. Its appearance suggests that this floating slob was once a normal human being, which went through a hideous mutation, growing a gigantic tumour from the abdomen, while the human being itself started to wizen in the process. It is unknown that the tumour was actually a distinctive life-form (or became one), or the fractured mind of the "host" controls this creature...it seems that the scrogged remains of the human being has no control over himself. The organs of the Diadron must be grown inside the balloon-like tumour, including the nervous system, if the Diadron has any. During the mutation, however, the Diadron have succesfully grown new kinds of organs inside - one of them sends powerful shockwaves towards the Diadron's prey, similar to electric eels, which can hardly be avoided, especially in close combats. Although the Diadron does not have any visible eyes, ears or nose, it can follow its victim around, preferably floating in mid-air (the Diadron can possibly sense the warmth of a body). Upon colliding with the prey, the Diadron is known to explode that instant - this proved to be lethal in most of the cases, so using close combat weapons is strongly discouraged. Apart from this, the Diadron appears to be quite resistant to gunfire, though it seems to be vulnerable for explosions, and Thermal Shok Launcher. The best choice is to keep yourself away from Diadrons, even their corpses - the ooze they leak may also cause harm, if stepped on without proper environmental protection.
Diadrons are very resistant to close combat, fire, and bullet weapons, but vulnerable to explosives, missiles, and high caliber guns.
So as you can see, if the "decoratedshit" is completed for the Diadron, it'll be quite a tough fella to beat - its hitscan attacks can hit you even from 50 km distance, and close combat weapons are unusable - in the moment you touch the Diadron, it would explode.
Well, this is the idea I have for a floating monster. If he wants a Pain Elemental...well, I might not be able to help...