The only useful card for Water-attribute monster deck that player can receive from level-up rewards is “Water Hazard” (Receive when reach level 25). However it is also possible to obtain that card from dueling him at the gate, so player do not spend too much time grinding his level.
Defeat him to farm drop skills
Most of the dueling reward cards that player could obtain from him are only useful to Water deck. The monster obtained from him are not so useful when compared to other Fish-type monster obtained from Age of Discovery pack. Still, it is not a suggestion that players should ignore dueling him, since the difficulty for beating his level 40 deck is not so hard, players could duel him to farm for the skill drop. → How to get drop skills
Mako Tsunami's skills
Note: More skills are expected! Report Skill name and details by submitting comments or screenshot at the bottom of the page.
Sea Stealth Activates if "Umi" is on your field. Monsters you have Normal Summoned, Special Summoned, or Flip Summoned become invisible to the opponent until end of their turn. If "Umi" leaves your field, all monsters become visible.
Draw Sense: WATER Can be used each time your Life Points decrase by 1500. In the Draw Phase, instead of doing a normal draw, draw a random Water-Attribute monster.
Balance Your starting hand will reflect the card balance of your deck.
Menace from the Deep Can be used if "Umi" is on the field, and you have a Water-attribute normal monster on your field. That monster can attack your opponent directly. this turn. At the end of the Battle Phase, that monster is sent to the Graveyard. This skill can only be used once per turn.
Mako Tsunami participates in many tournaments so that he can use the prize money to buy a fishing boat and sail the mighty waves. He masterfully used his Sea Deck to give Yugi and Joey some of the toughest Duels ever. His signature monster "The Legendary Fisherman" unleashes its true strength when it swims out into his "Umi" field.
When you think about it, most of the known major tournament duelists that were such before the start of the series are kind of messed up, aside from Mako. Kaiba was pretty sadistic, Keith was... destroyed by Pegasus beating him, Weevil was dishonest even before Yugi beat him, Mai was super-depressed... I guess Rex and Rebecca weren't too bad.