Encounter 13 - lvl 5 to 10

2x Gibbering Mouther Medium aberration , neutral
Armor Class 9 Hit Points (9d8 + 27) Speed 10 ft., swim 10 ft.
STR 10 (+0) DEX 8 (-1) CON 16 (+3) INT 3 (-4) WIS 10 (+0) CHA 6 (-2)
Condition Immunities Prone Senses Darkvision 60 ft., Passive Perception 10 Languages -- Challenge 2 (450 XP) Proficiency Bonus +2
Aberrant Ground. The ground in a 10-foot radius around the mouther is doughlike difficult terrain. Each creature that starts its turn in that area must succeed on a DC 10 Strength saving throw or have its speed reduced to 0 until the start of its next turn.
Gibbering. The mouther babbles incoherently while it can see any creature and isn't incapacitated. Each creature that starts its turn within 20 feet of the mouther and can hear the gibbering must succeed on a DC 10 Wisdom saving throw. On a failure, the creature can't take reactions until the start of its next turn and rolls a d8 to determine what it does during its turn. On a 1 to 4, the creature does nothing. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can't make such an attack.
Actions Multiattack. The gibbering mouther makes one bite attack and, if it can, uses its Blinding Spittle.
Bite. Melee Weapon Attack: +2 to hit, reach 5 ft., one creature. Hit: (5d6) piercing damage. If the target is Medium or smaller, it must succeed on a DC 10 Strength saving throw or be knocked prone. If the target is killed by this damage, it is absorbed into the mouther.
Blinding Spittle (Recharge 5–6). The mouther spits a chemical glob at a point it can see within 15 feet of it. The glob explodes in a blinding flash of light on impact. Each creature within 5 feet of the flash must succeed on a DC 13 Dexterity saving throw or be blinded until the end of the mouther's next turn.
3x Hell Hound Medium fiend , lawful evil
Armor Class 15 (Natural Armor) Hit Points (7d8 + 14) Speed 50 ft.
STR 17 (+3) DEX 12 (+1) CON 14 (+2) INT 6 (-2) WIS 13 (+1) CHA 6 (-2)
Skills Perception +5 Damage Immunities Fire Senses Darkvision 60 ft., Passive Perception 15 Languages Understands Infernal but can't speak it Challenge 3 (700 XP) Proficiency Bonus +2
Keen Hearing and Smell. The hound has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Pack Tactics. The hound has advantage on an attack roll against a creature if at least one of the hound's allies is within 5 feet of the creature and the ally isn't incapacitated.
Actions Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: (1d8 + 3) piercing damage plus (2d6) fire damage.
Fire Breath (Recharge 5–6). The hound exhales fire in a 15-foot cone. Each creature in that area must make a DC 12 Dexterity saving throw, taking (6d6) fire damage on a failed save, or half as much damage on a successful one.