The main commander in this deck is Morska, Undersea Sleuth, great legendary creature that comes with all sorts of abilities
Honorable Mentions Amethyst Chromicon has the drawback of aiding your opponent but adds a lot of consistency
Some of the spells destroy creatures, others exile them, and recently, blue has gained the ability to remove artifacts (see Ravenform)
If you want something a bit smaller in scale, cards like Sparkmage Apprentice, Ghitu Shaman, and Basalt Ravager can really bring the beats
Pls note I didn't include things from Monster Hunter Frontier or Online (except one location out of necessity) since there was never a North American release for these games and never will be be
He can play with lifelink to gain a bunch of life for attackers and then tap for it post-combat to make cheap stuff without spending any mana at all to get started