Crystalin

Stage one virus 1d4 weeks- +5 health +1 AC Crystal breath attack 

Stage two virus 3d4 weeks- regeneration (if not hit for one round heal 2d6 health) hunting eyes (any creature within a 25ft radius it can detect) x2 health x2 damage dice, challenge is now 3

Stage three 2d8 weeks- x2 health +2 damage dice +10ft movement speed, legendary actions unlocked. Challenge is now 7

Claw- 5ft reach, +3 to hit, hit (2d6 bludgeoning damage)

Crystal Breath- 10ft cone, Dex 14 save to take half damage, hit (1d8 radiant damage), make Con save (16) every 2 hours or take 2d6 necrotic damage, after 10 hours have passed without saving become this creature. Recharge 5-6

Imbue 1 legendary action- deal an extra 2d4 radiant damage next claw attack.

Crystal Calling 2 legendary actions- all Crystalins within 60ft are now under it’s control, they also get +1 to hit.