n large animal aquatic 

Perception +6; darkvision, scent (imprecise) 30 feet

Skills Acrobatics +4, Athletics +7

Str +4 Dex +1 Con +4 Int -4 Wis +3 Cha +1

AC  16; Fort +9, Ref +4, Will +6

HP 24

Buck [R] DC 17

Speed 5 feet, swim 40 feet

Melee [>] tail +7 (reach 10 feet), Damage 1d6+4 bludgeoning

Sudden Retreat [>>] The hippocampus makes a tail Strike, then Swims with a +10-foot circumstance bonus to its swim Speed. It gains a +2 circumstance bonus to AC against reactions triggered by this movement.

Bestiary 2, page 142.