Alcohol Explosion: Upon death, Keg Mimic explodes with whatever liquid is inside.  Everyone within a 10ft radius must make a DC 10 Dexterity saving throw or be covered with the liquid.  No other effects happen

False Appearance. While the keg mimic remains motionless, it is indistinguishable from an ordinary keg or barrel.

Keg Punch: Melee Fist Attack: +1 to hit, reach 5ft, 1 target. Hit: 1 (1d4 +1) [bludgeoning damage]

Action Ale Belch: Keg Mimic spews toxic ale (or other liquid) ranged attack +4 to hit, range 5ft/30ft, 1 target.  Hit: 1 (1d6 +1) [poison damage] 

Mud Breath (Recharge 6). The Keg Mimic belches viscid Ale onto one creature within 5 feet of it. If the target is Medium or smaller, it must succeed on a DC 11 Dexterity saving throw or be restrained for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.