Basic combo is to summon saryuja, aim for 2 lv4s to make bahamut shark, use bahamut to summon rebarian shark, overlay rebarian shark for armored black ray lancer, summon f0 future slash, overlay it to utopic future dragon. Any extender can be used to summon predap anaconda for dragun of red-eyes and frog extenders for toadally awesome. If u didnt have extender for predap/toadally, it means ur deck is still stacked with rank-up 7th on the top thanks to rebarian shark, therefore you can summon c101 directly next turn (SHARK INTENSIFIES). With MR5 coming, the bahamut shark spam version is better than this mermail variant, so I have to put this in non-meta category.
Most of the cards are just to summon saryuja while being water and lv4.
Complimentary cards: dark magician (fusion material), vanilla red-eyes (fusion material, following the new archetype fusion ruling), red-eyes fusion (predap target), moray and salvage (for the plus), called by the grave (negates monster handtrap), abyss-scale mizuchi (negates spell, esp super poly if it's the first spell used).
Extra deck: basic combo cards. dracossak and linkuriboh are used just in case u have monster with the same name (lv7s or lv1s) so u can summon saryuja.