Corrupt Marsh Moccasin

Crystal Corruption: Due to the crystals embedded in the body, the Corrupt Moccasin has an increase to AC of +7

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 8 (1d4 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one.

Acid Spit. Ranged Attack: +8 to hit, reach 30 ft., one target or 2 targets within 5ft of each other.  The Marsh Moccasin spits a bubble of acid. Choose one or two creatures you can see within range. If you choose two, they must be within 5 feet of each other. The target takes 5d6 acid damage.

Tale Whip. Melee attack, 10ft. +8 Hit.  The March Moccasin may use it's tail to whip a creature in range for 1d6 damage. 

Shriek.  20ft radius, Recharge 5-6. Taken over by madness, the corrupt marsh moccasin screams. Each creature in a 20-foot-radius sphere centered on the monster must make a Constitution saving throw (DC 15). A creature takes 5d8 psychotic damage on a failed save, or half as much damage on a successful one.