Spree

Small Fiend chaotic evil

STR	DEX	CON	INT	WIS	CHA
11 (+0)	17 (+3)	16 (+3)	10 (+0)	8 (-1)	15 (+2)

Saving Throws: Dex +6, Wis +2
Skills:
Damage Immunities: poison
Damage Resistances: cold, fire, lightning; bludgeoning, piercing, and slashing from nonmagical attacks
Condition Immunities: frightened, poisoned
Senses: darkvision 60 ft., passive Perception 9
Languages: Abyssal, Common, Gnomish

Frothing Rage: The spree demon has advantage on attacks if it saw another spree demon make a successful attack within the last minute.
Spree Madness: If a creature confused by the spree demon's claw attack reduces a target to 0 hp, the confused creature must make a successful DC 14 Wisdom saving throw or gain a short-term madness (see the System Reference Document 5.1). If a creature fails this saving throw again while already suffering from a madness, it gains a long-term madness instead.

Multiattack: The spree demon makes two claw attacks. If both attacks hit the same target, the target must succeed on a DC 14 Wisdom saving throw or become frightened for 1 minute. While frightened this way, the creature believes it has shrunk to half its normal size. All attacks against the creature do an extra 7 (2d6) psychic damage, and the creature's attacks do half damage. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Claw: Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) slashing damage plus 10 (3d6) poison damage, and the creature must make a DC 14 Constitution saving throw. On a failure, the target can't take reactions and must roll a d10 at the start of each of its turns to determine its behavior for that turn for 1 minute. This works like the confusion spell. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to this effect for the next 24 hours.