Lithe Form. The Hydralisk has advantage on Dexterity saving throws as long is it can see the attack and isn't restrained.

Extreme Poison Proficiency. The Hydralisk has advantage on melee attacks against any creature that is poisoned.  

Grappled Bite. If the Hydralisk hits with a Scythe attack it grapples the target and immediately bites them.

Multiattack. The Hydralisk makes two Scythe attacks.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 4 (1D4 + 3) Piercing damage and 4 (1D8) Poison damage and must succeed on a DC 12 Constitution saving throw or be poisoned for 1 minute.

Scythe. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (2d6 + 3) Slashing damage. 

Spines. Ranged Weapon Attack: +4 to hit, range 60/120 ft., one target. Hit: 5 (1d6 + 2) Piercing damage and 4 (1D8) Poison damage and must succeed on a DC 12 Constitution saving throw or be poisoned for 1 minute.

Return Fire. If a target misses with a range attack the Hydralisk can immediately make a ranged attack at that target.