Amphibious. The beast can breathe both air and water. Beast Bond. You can add your proficiency bonus to any ability check or saving throw that the beast makes.
Binding Strike. Melee Weapon Attack: STR mod. + PB to hit, reach 5 ft., one target. Hit: 1d6 + 2 + PB piercing or bludgeoning damage (your choice), and the target is grappled (escape DC equals 8 + STR mod. + PB). Until this grapple ends, the beast can't use this attack on another target.