Undead Fortitude. If damage reduces Adrion to 0 hit points, he must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, Adrion drops to 1 hit point instead.

Shapechanger. Adrion can use an action to polymorph into a Small or Medium humanoid he has seen, or back into his true form. His statistics, other than his size, are the same in each form. Any equipment he is wearing or carrying isn't transformed. He reverts to his true form if he dies.

Spellcasting. Adrion is a 7-level spellcaster. His spellcasting ability is [Intelligence] (spell save DC 14, + 6 to hit with spell attacks). Adrion has following [class name] spells prepared:
Cantrips (at will): [Fire Bolt], [Mage Hand], [Prestidigitation], [Ray of Frost] 
1st level (4 slots): [Detect Magic], [Magic Missile], [Shield]

2nd level (3 slots): [Invisibility], [Mirror Image], [Scorching Ray]

3rd level (3 slots): [Counterspell], [Fireball], [Lightning Bolt]

Action Name. Dagger

Action Melee Attack. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 2 (1d4 + 2) [piercing] damage. 

Action Name. Fire Bolt

Action Ranged Attack. RangedWeapon Attack: +6 to hit, range 120 ft., one target. Hit: 14 (4d#10) [fire] damage.

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Reaction Name. Enter the description for your action.

Adrion can take 2 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Adrion regains spent legendary actions at the start of his turn.

Casts Cantrip (Costs No Actions). Simply casts one of his cantrips.

Move (Costs No Actions). Adrion moves up to his speed without provoking opportunity attacks.

Spell(Costs No Actions). Adrion casts a spell using a spell slot.

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Mythic Action Name (Costs # Actions). Enter the description for your mythic action.