Legendary Resistance (3/Day). If Karen fails a saving throw, she can choose to succeed instead.
Magic Weapons. Karen's weapon attacks are magical.
Multiple Heads. Karen can take one reaction per turn, rather than only one per round. She also has advantage on saving throws against being knocked unconscious.
Regeneration. Karen regains 30 hit points at the start of her turn.
Multiattack. Karen makes three attacks: two with her claws and one with her tail.
Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 24 (4d6 + 10) slashing damage.
Tail. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 28 (4d8 + 10) piercing damage.
Legendary Actions
Karen can take 2 legendary actions per head(6 actions), choosing from the options below. Only one head can be used for a legendary action option at a time, and only at the end of another creature's turn. Karen regains spent legendary actions at the start of its turn.
Karen's legendary action options are associated with her three dragon heads (a bite and a breath weapon for each). Once Karen chooses a legendary action option for one of her heads, she can't choose another one associated with that head until the start of her next turn.
Bite. Melee Weapon Attack: +9 to hit, reach 20 ft., one target. Hit: 12 (2d10) slashing damage plus 14 (4d6) lightning damage (blue dragon head), fire damage (red dragon head), or cold damage (white dragon head).
Blue Dragon Head: Lightning Breath (Costs 2 Actions). Karen breathes lightning in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 88 (16d10) lightning damage on a failed save, or half as much damage on a successful one.
Red Dragon Head: Fire Breath (Costs 2 Actions). Karen breathes fire in a 90-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.
White Dragon Head: Cold Breath (Costs 2 Actions). Karen breathes an icy blast in a 90-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 72 (16d8) cold damage on a failed save, or half as much damage on a successful one.