Chatacabra

Amphibious. The chatacabra can breathe air and water.

Standing Leap. The chatacabra's long jump is up to 20
feet and its high jump is up to 15 feet, without a
running start. In addition, the chatacabra does not
provoke opportunity attacks while moving with a jump.

Multiattack. The chatacabra makes two Fist attacks. It
can replace one of these attacks with a Lick attack.

Fist. Melee Weapon Attack: +4, reach 5 ft., one
target. Hit: 9 (2d6 + 2)

Lick. Melee Weapon Attack: +4, reach 10 ft., one
target. Hit: 11 (2d8 + 2)

Deadly Leap. If the chatacabra jumps at least 15 feet as
part of its movement, it can then use this action to
land on its feet in a space that contains one or more
other creatures. Each of those creatures must succeed
on a DC 12 Strength or Dexterity saving throw (target's
choice) or be knocked prone and take 12 (3d6 + 2) On a successful save, the creature takes only half the damage, isn't knocked prone, and is pushed 5 feet out of the chatacabra's
space into an unoccupied space of the creature's
choice. If no unoccupied space is within range, the
creature instead falls prone in the chatacabra's space.

Arm Lick (Recharge 4-6). The chatacabra licks its arms,
coating them with saliva infused with the surrounding
terrain. Until the start of its next turn, the damage type
of the chatacabra’s Fist attack changes according to
the terrain (see Monster Manual table). Additionally, the target
must succeed on a DC 12 saving throw (type found in
the table) or suffer the condition specified for that
terrain for 1 minute unless otherwise specified.

The chatacabra can take 2 legendary actions, choosing
from the options below. Only one legendary action
option can be used at a time and only at the end of
another creature's turn. The chatacabra regains spent
legendary actions at the start of its turn.
Detect. The chatacabra makes a Wisdom (Perception)
check.
Charge (Costs 2 Actions). The chatacabra moves up to
half its speed. Then makes one Lick attack.
Smash (Costs 2 Actions). The chatacabra slams its fist
on the ground. Each creature in a 15-foot cube
originating from the chatacabra must succeed on a DC
12 Strength saving throw or be pushed 5 feet away.