5E Platypus

[Yunru]

This is my first attempt (that I remember) at creating a monster, so feedback most welcome.

Giant Platypus:
Large Beast, Neutral
Challenge 2 (450 Exp)
Speed 30, Swim Speed 30
Immunity: Poison
Vision: Darkvision 30"
STR 8 DEX 16 CON 14 INT 10 WIS 13 CHA 10
AC 13 HP 55(10d8+10)
Amphibious: The Platypus can breathe air and water.
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 12 (2d8+3) piercing damage, and the target must succeed on a DC 14 Constitution saving throw or take an additional 18 (5d6) Poison damage.

 

[The Glen]

Is its a giant platypus? Instead of giving it gills, just say it can hold its breath for an extended period of time, like 10 minutes

 

[Yunru]

It wasn't giant but it n9w is.

 

[TwoSix]

That is one semi-aquatic egg-laying mammal of action.

 

[Tia Nadiezja]

Here's a different layout for the Platypus's attacks:

Multiattack. The giant platypus makes one Bite and one Spur attack.

Bite. Melee attack, reach 5'. +5 to hit, one target. Hit: 1d8+3 Piercing damage.

Spur. Melee attack, reach 5'. +5 to hit, one target. Hit: 1d8+3 piercing damage, and the target must make a DC 14 Constitution saving throw or take 3d8 poison damage and become poisoned.

Platypi don't have toxic bites - they inject their venom through a spur on the hind leg.

ADDENDUM: No need to give it limited time holding its breath - basically all creatures that live heavily in water in the DMG are just given the Amphibious feature, since their breath-holding time is long enough that it's irrelevant that they eventually need to surface to breathe in game terms. Giant platypus definitely fits that, though if one were to stat out the basic platypus (which would be a CR 0 creature worth 10 XP with a poison sting dealing 1 damage and the Poisoned condition), it would lack Amphibious. Real platypi dive for 40 seconds at most.

 

[Coronoides]

New trait idea inspired by history: Obviously a hoax: Any character seeing a giant platypus for the first time must make a INT save DC10 or treat the platypus as an illusion until evidence breaks this belief. While disbelieving in the platypus the character suspects her senses and receives advantage on saves against actual illusions.
Other stuff
Maybe bludgeoning damage for the bite representing the duck bill?
If you have a bite and spur then you might add multiattack