Calderbeam

Special Trait Name. It is huge and has camouflage to sneak up on its prey and the ones trying to slay tend to get slain instead.

Spellcasting. The [Calderbeam] is a 21-level spellcaster. Its spellcasting ability is [17] (spell save DC 20, +5 to hit with spell attacks). The [Calderbeam] has following [Celestial] spells prepared: Alter reality, major creation

Cantrips (at will): [magic bolt], [mask] 
1st level (5 slots): [rescue], [Phantasmul force] (Chromatic orb)(read illusionist magic )(light)

Action Name. sprays acid from its breath doing 25 damage

Action Melee Attack. Melee Weapon Attack: +10 to hit, reach #60ft., 18 target. Hit: 20 (1d20 + 10) [breath] damage. 

Action Ranged Attack. Ranged breath Attack: +#10 to hit, range 70/60 ft., 5 target. Hit: 2 (1d20 + 10) [breath] damage. 

Hit points. 

Enter the description for how bonus actions work for your monster here. It gets to go twice on its first turn!

Reaction Name. if you touch it it will try to shred you to pieces and become more vicious than ever after you attack it

Is not legendary.

Enter the description for how mythic actions work for your monster here. it opens its mouth and acid spills out all over 3 adventurers in the group get paralyzed until the monster was dead or 5 turns had passed 

Mythic Action Name (Costs 5 Actions). Acid splatter