Crystal Dragon Egg

Impressionable. The Dragon will hatch at some point, it is still young and impressionable. If the Egg witnesses any evil actives the Dragon will have a chance to hatch into a Void Dragon. If it witnesses heroism and good deeds it will hatch into a Glass Dragon.

Spellcasting. The Egg is a 5-level spellcaster. Its spellcasting ability is CHA (spell save DC 15, +5 to hit with spell attacks). The Egg has following spells prepared:
Cantrips (at will): Sending, Scry, Detect Thoughts, Suggestion 
Once per day it can cast Fly and gains 30 ft of fly speed lasts for 6 hours.

STOP! As a reaction to being attacked it can use it's reaction to cast Time Stop. Pg 283 PHB

Harden. The Egg may willingly harden it's shell with glass that the creature produces from the inside. raises AC to 30. ONLY usable if surrounded by good aligned characters.

Squish. The creature, lowers it's AC to 10, but gains 50 HP and deals 6d6+6 poison damage to anyone or anything touching it. ONLY usable if surrounded by neutral or evil characters.

STOP! As a reaction to being attacked it can use it's reaction to cast Time Stop. Pg 283 PHB

Enter the description for how legendary actions work for your monster here.

Impressionable mind. Once per Day the DM decides if the creature takes a point in the good or evil Alignment, if the creature reaches a certain point in either category it will hatch into a different dragon of the DM's decision. If the DM deems a deed worthy it could be worth more than one point in either good or evil, i.e. If the party saves a family from a burning barn it may be worth 30 points in the good category, while murdering the local guards for standing up for themselves may award -30 points in the evil category. If after one year the dragon still hasn't hatched the spirit of the animal will die and wither away, with a small chance of summoning a DracoLitch in its place.