Creature of the Deep

Amphibious. Creature of the Deep can breath in both water and air.

Creature of the Deep contains action-oriented abilities, which can be done on initiative 0: 

1st round: Creature of the Deep moves an additional 30ft without causing opportunity attacks

2nd round: Creature of the Deep moves an additional 15 ft., and does a bite attack. After biting, it rolls in its place, dealing 21 (6d6) piercing damage.

3rd round: Creature of the Deep submerges underwater and attempts to hide ( it gains an extra +5 to its Stealth roll). Additionally, it gains 50ft swim speed.

Multiattack. Creature of the Deep makes two attacks: one with its bite and one with its tentacle.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 14 (2d10 + 2) piercing damage and 7 (1d10 + 1) acid damage.

Tentacle. Melee Weapon Attack: +8 to hit, reach 10 ft., one target not grappled by the crocodile. Hit: 14 (2d8 + 5) piercing damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or be poisoned.

Tentacle Wrap. Creature of the Deep lashes out with (Recharge 5-6), and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and Creature of the Deep can't wrap another target.

Disappearing charge. As a bonus action, Creature of the Deep flattens its body into shallow water, gaining an extra 20ft swim speed, +5 stealth, and can move through hostile creatures until the end of the turn. Those creatures must make a DC 12 Dex save or be knocked prone. Creature of the Deep can only knock creatures prone if they are both in the water.