Crackleburr

Engorgement. Crackleburr is composed of primal blue and red lightning. When a spell of third level or higher is cast within Crackleburr's sight. It can choose to increase its size category by one for 1 minute. Each time Crackleburr is engorged, its attacks deal an additional 1d10 lightning damage and its movement speed increases by 30 feet.

Elemental Form. Crackleburr can move through a space as narrow as 1 inch wide without squeezing.

Lightning Fox. Crackleburr is immune to being charmed or frightened, and can't be targeted by any divination magic or perceived through magical scrying sensors.

Multiattack. The elemental makes one Lightning Bite attack and one Lightning Tail attack. Or it can use its lightning storm.

Lightning Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: (2d10 + 5) Lightning damage.

Lightning Tail. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: (2d8 + 4) Lightning damage

Lightning Storm. If Crackleburr is large or bigger, it can unleashes a storm of lightning bolts in a 60-foot radius centered on itself. Each creature in that area must make a DC 18 Dexterity saving throw, taking 66 (12d10) lightning damage on a failed save, or half as much damage on a successful one.
Each use of Lightning Storm reduces the size category of Crackleburr by one.

Blue Engorgement: When a creature within 30 feet of Crackleburr casts a spell that deals cold, acid, or lightning damage, Crackleburr can expend a reaction to absorb some of the energy. The creature casting the spell can choose to either increase the damage of the spell by 2d8 or gain a fly speed of 30 feet until the end of their next turn.

Red Engorgement: When a creature within 30 feet of Crackleburr casts a spell that deals fire or thunder damage, Crackleburr can expend a reaction to absorb some of the energy. The creature casting the spell can choose to either increase the damage of the spell by 2d8 or push a target of their choice within 30 feet of them up to 30 feet away, pending a DC 18 Strength Check.