So it's special summon by discarding 2 water monsters and when it's special summoned like that, I get to add an "Abyss-" spell or trap card to my hand. Question is I dunno if they have the TCG rulings or not but is the special summon a summoning condition like Moulinglacia where TKRO can negate it or is Abyssmegalo's Special Summon an ignition effect since it's effect goes off right after it's special summoned that way
OP, learn to PCCT.
"You can discard 2 other WATER monsters; Special Summon" means that it is an Ignition effect. You reveal it in your hand and discard 2 other WATERs. Your opponent can respond, and if it is not negated, Abyssmegalo is summoned.