Barnacle Grenade

This heavy, coral-crusted sphere is sealed with dormant barnacle spores and calcified growths. When shaken, faint scraping can be felt beneath its surface.
As an action, you can throw the grenade at a creature you can see within 60 feet. When the grenade strikes its target, it bursts open, releasing a violent surge of accelerated barnacle growth.
The target must succeed on a DC 20 Strength saving throw or become restrained as jagged barnacles rapidly encase its body. While restrained in this way, the creature is incapacitated and can’t move.
A creature restrained by the barnacles can use its action to make a DC 20 Strength (Athletics) check, ending the effect on a success. The barnacles can also be destroyed; they have AC 19, 20 hit points, and are immune to poison and psychic damage.
Once the barnacle growth is destroyed or removed, the grenade is rendered inert and becomes a mundane coral husk.
The barnacle growth functions normally underwater and adheres instantly to flesh, armor, or stone.
Throwing this while underwater does not incur disadvantage.