Astral Sturgeon

Saving Throws:

Advantage on spell saving throws.

Advantage on all checks to escape a grapple.

Water Breathing: This creature can only breathe underwater.

Astral Jumping: Astral Sturgeons can jump through planes like a regular fish jumping out of water.

Planar Fishing: Only a Planar Pole can stay attached to an Astral Sturgeon while it travels between planes.

Action Name. Struggle: The Astral Sturgeon attempts to break free of any fishing line, double its movement speed and deals 13 points of slashing damage to any line and tackle currently being used on it. Recharge: 1d4-1

Action Melee Attack. Tail slap: +6 to hit, reach 10 ft., 1 target. Hit: (4d8 + 6) [bludgeoning] damage. Upon making this attack, the creature can travel half it's movement speed in the opposite direction in which this attack was done. This attack also lets it attempt to escape any grapple it is currently in.

Tug and Pull: This creature may use its reaction to halve the distance a fishing line would pull it in. 

Scale Scrape: When a creature tries to grapple this fish, it may use its reaction to puff up and increase its AC by 3 and deal 13 points of slashing damage to whatever is attempting to grapple it.

Legendary actions:

Astral Jump:  Roll 1d6 to determine which plane you jump to;

1-Material Plane

2-Astral Plane

3-Plane of Water

4-Plane of Light

5-Ethereal Plane

6-Feywild

Recharge: 1d4-1

Tabard Transformation: Upon being caught and being held on land for 5 rounds, the Astral Sturgeon enters the final phase of its life and transforms into the Tabard of the Sturgeon magical item and automatically attunes (if possible) to the one who caught it. In doing so it releases its eggs to every plane on the Planar Jump list where new Astral Sturgeon will grow and mature to repeat the process all over again.