Basilisk Hatchling

Growth: The Hatchling gains 1 growth point for each level it gains (party level). On each level up you can spend a number of points 

Growth Stages. 

Moderate venom (1). The poison damage die from the bite attack of the Basilisk becomes a D6 instead of a D4

Potent Venom (2). The poison damage die from the bite attack of the Basilisk becomes a D10 instead of a D6 (requires better venom)

Stone Resilience (2). The Basilisk gains resistance to non-magical weapon attacks (slashing, piercing, bludgeoning)

Moderate Gaze (2). DC becomes a 15 Con Save. Success or fail, the target has to repeat the save at the start of each of its turns until it has either 3 success or 3 failures, whichever comes first. On 3 success, this effect ends. On 3 failures, the creature is petrified for 1 hour. Can be used a number of times per long rest equal to half the proficiency modifier.

Potent Gaze (3). The DC for petrifying gaze becomes 18 Con save. Creatures who fail twice are petrified permanently, until cured by a greater restoration or Wish spell. (require moderate Gaze)

Growth I (3). The hatchling becomes a full grown basilisk. Its size grows to medium (dire wolf size). Its STR becomes 18, Dex becomes 10 and Con becomes 15.  Its Hit die becomes a d10 and gains 3 hitpoints for each level it already has.

Growth II (3). The basilisk becomes a larger than . Its size grows to Large ( ___ ). Its STR becomes 20, Dex becomes 12 and Con becomes 17.  Its Hit die becomes a d12 and gains 3 hitpoints for each level it already has. (require Growth I)

Deflective Aura (3).  The basilisk's scales shimmer with a magical aura that grants it a reflective shield. When attacked with a ranged spell attack, the basilisk can make a STR Save equal to the attack roll. On a success it reflects the spell back at the attacker, using the original spell attack roll against them. This can be used once per short rest.

Arcane Amplifier (4). The basilisk can channel and amplify spells cast by its master. Once per short rest, the master can increase the spell slot level of a spell by one when cast through the basilisk (e.g., a 3rd-level spell slot becomes a 4th-level slot).

Shadowstep I (2). The basilisk can meld into shadows and reappear from another shadow within 30 feet. This is a bonus action and can be used up to once per short rest

Shadowstep II (1). The basilisk can take up to 1 willing creature in its shadowstep. Usage becomes twice per short rest. (requires shadowstep I) 

Regenerative Scales (2). The basilisk can heal itself by shedding and regrowing its scales. It can use an action to regain hit points equal to 1 hit die + its Constitution modifier. This ability can be used half the number of proficiency  per short rest (rounded up).

Healing Scales (3). The basilisk can transfer some of its regenerative power to its master of allies. By touching a creature, it can grant 2x its hit die as temporary hit points. In addition, that ally gains +2 AC bonus as long as those temporary hit points remain. (requires Regenerative Scales)

Vine Whip (1): The basilisk can control nearby plant life to lash out at enemies. As an action, it can command vines to grapple a creature within 30 feet. The target must make a DC 15 Strength saving throw or be grappled until the end of its next turn. Usable once per short rest.