After getting zapped by the trident, Damon feels nothing at first, but then looks back at his legs, as they start growing dark navy blue scales that start at his waist, and crawl down to the bottom, covering his entire legs with blue scales. Just then, Damon's limbs start to inflate like a child's muscle suit, but more realistic.
Damon even started getting taller, as muscles grew on his arms, and chest, as his abs became big, and revealing. Once Damon has gained an 8 pack of abs, along with large pecks, he feels his face growing facial hair, and it extends into a long beard the same color as his own hair, while the back of his own hair extends with it. Finally, as the scales on his legs reach the heels, the bones in Damon's legs readjust themselves, while his feet flatten, and turn into a long blue tail fin completing his transformation.
Damon took a look at himself after he was finished changing. Damon now had a muscular body, that ended in a navy blue merman's tail, but was curious if his privates were still there. Damon then finds his testicles have expanded, while a long penis pops out of the shaft.