Large Beast
Armor Class 13
Hit Points 22 (4d10)
Speed swim +40, walk +0
Challenge 1/2
Senses passive Perception 11
Water Breathing. The seahorse breathes only water.
Ram. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 6 (2d4+1) bludgeoning damage. If the seahorse moves at least 20 feet straight towards the target before the attack the attack deals an extra 5 (2d4) bludgeoning damage and the target makes a DC 11 Strength saving throw falling prone on a failure.
Source: Level Up Advanced 5e Monstrous Menagerie · OGL/Open