Basi-lich

Humanoid form

This form is the creature's preferred appearance and helps the lich maintain control over the beast within. This appearances resembles the lich prior o this unholy fusion. This form has an AC of 13 and 1/2 the Hp of its true form and can perform Petrifying touch as a melee spell attack. When defeated in this form it immediately reverts to it's true form with full Hp any damage received carries over

True form

Petrifying Gaze. If a creature starts its turn within 30 feet of the basilisk and the two of them can see each other, the basi-lich can force the creature to make a DC 16 Constitution saving throw if the basi-lich isn't incapacitated. On a failed save, the creature magically begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.

A creature that isn't surprised can avert its eyes to avoid the saving throw at the start of its turn. If it does so, it can't see the basi-lich until the start of its next turn, when it can avert its eyes again.

If it looks at the basi-lich in the meantime, it must immediately make the save. If the basi-lich sees its reflection within 30 feet of it in bright light, it mistakes itself for a rival and targets itself with its gaze.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 10 (2d10+ 3) piercing damage plus 7 (2d6) poison damage.

Petrifying Touch. Melee Spell Attack: +9 to hit, reach 5 ft., one creature. The target must succeed on a DC 16 Constitution saving throw or be petrified for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Spellcasting. The basi-lich can cast spells in either form and is an 11th-level spellcaster due to it's degraded intelligence. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). The basi-lich has the following wizard spells prepared:

Cantrips (at will): mage hand, prestidigitation, ray of frost

1st level (4 slots): detect magic, magic missile, shield, thunderwave, mage armor

2nd level (3 slots): acid arrow, detect thoughts, invisibility, mirror image

3rd level (3 slots): animate dead, counterspell, dispel magic, fireball

4th level (3 slots): blight, dimension door

5th level (2 slots): mislead, scrying

6th level (1 slot): flesh to stone, globe of invulnerability

Turn Resistance. The basi-lich has advantage on saving throws against any effect that turns undead.

Animal Fury. When below half health in its beast form it makes a wisdom saving throw (DC 13) for the lich to remain in control. When attacked the DC increases by 2 and must make another save. If failed the Basilisk soul takes over in a rage and it can now do 2 attacks a round. Spells cannot be cast in this form.

Savage Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 10 (2d12+ 5) piercing damage plus 7 (2d6) poison damage. (Only usable when Animal Fury is in effect)