lets take a look at this decks engine first shall we,
abyss-megalo, this card is the first engine of this deck sp summons right from your hand just dump two other water monster, which should be relatively easy because every monster in this deck should be water. It is a level 7 beater and its well worth the discard eff.
abyss-teus, this is the second engine of this deck, its also a level 7 with relatively small attack numbers but combine with other abyss monsters its perfect the way it is. Now don't get ahead of yourself running this in threes because only one can sp summon at a time off of his eff, so keep it classy run it in ones and two's
abyss-linde, is the third engine making level seven mermails easy as heck to get out for a ftk (first turn and four turn kill) version of this deck... All abyss deck run in threes but be careful only one gets its eff per turn.
atlantean dragoons, not a mermail but a ghastly eff to run with these abyss monsters, if its sent to the grave for the eff of a water monster you can add any sea serpent to your hand from the deck. that's so great with these monsters its just what they need. In a full abyss run 1-3 in a water deck version run 1-3 I would say three this guy is just too good.
abyss-gunde, this card is so broken if its discarded from the hand to the grave by the eff of a water monster it allows you to sp summon a mermail monster from your grave, i.e. megalo linde and teus standard build run 1-3 in a water deck 0
abyss-soldier no one pays attention to this guy but I do, so I would say any version of this you are running whether its the standard build or atlanteans I would say run three of this guy because with gunde he makes it so she will have a target in the grave and it returns a card on the field to the owners hand and with dragoons it returns a card on the field to the owners hand helping the megalo you get off of dragoons eff go off without a sinch.
you decide if you want to use the other artlanteans... they are great cards just meaningless in attack.