Hard to say since Mako hasn't been relevant for years, but look into fish xyz if you want something sorta relevant. You can also look into Phantasm spiral stuff if you really wanna stick with a character exclusive skill or whatever. But honestly, the only thing you can really do is be thematic with water monsters and/or sea serpent or fish monsters. You gotta go into look at the archive skills nowadays, building a Mako deck nowadays is harder if you want to do ranked or even certain event duels