Spawn of Tiamat

Spoiler: Greenspawn Razorfiend
Large Monstrosity
Armor Class 13
HP 150
Speed 50 ft, swim 50 ft
Str +4, Dex +3, Con +3
Int -1, Wis +1, Cha -2
Skills Athletics +7, Perception +4
Immunities poison; poisoned
Senses darkvision 60 ft
Languages Infernal
CR 7 (2900 XP)
Amphibious. The razorfiend can breathe air and water.
Spring Attack. The razorfiend can take the Disengage action as a bonus action on its turn.
Multiattack. The razorfiend makes three attacks: two with its wingblades and one with its bite.
Wingblade (melee) +7: 2d10+4 slashing + 1d8 poison; crit. 19-20
Bite (melee) +7: 2d10+4 piercing
Poison Breath (Recharge 5-6, 20-ft cone): 10d8 poison (Con DC 15 half)

Encounter Composition
Greenspawn Razorfiend

XP Award: 2900


Needs playtesting to make sure it's a good fight with a solo monster.