They are green platypuses with large black eyes. The leader wears a black helmet, gloves, boots, and cape, and orders all the others to fulfill his deeds. They tend to make duck-like quacking noises when they talk. Their powers include glowing, levitation, mind control, shooting acid.
They also carry deadly ray guns. In Season 63, they would undergo a change in their design; having spiked tails, antennae, and longer bills with sharp teeth. They will also have new powers and abilities.
Their main goal is to destroy the world and/or turn all the HTFs into their slaves.
- Splendid's Space Adventure
- Gangsters and Aliens
- Break of the Platypi (Ka-Pow!)
- Fall Problem
- Blast Off
- E.T.M. (Extra Terrestial Monotreme)
- U.F.M. (Unidentified Flying Monotreme)
- Out of this World
- Warning - One dies from an unknown cause, the leader and the others are devoured by zombies.
- Gangsters and Aliens - Shot by Al Capone, the leader is pushed into a pit.
- Splendid's Space Adventure - One is vaporized, the rest are killed by Splendid.
- Break of the Platypi - Some are crushed on a ship by steps; two are splattered on a broken building; some are hit by pieces of a broken ship by Lary and Mary.
- Fall Problem - Young platypus alien is impaled by leaves; ship crashes; platypus aliens smashed by ship.
- Blast Off - Some burn from melted cheese, others crash into an asteroid.
- E.T.M. (Extra Terrestrial Monotreme) - Melted by water.
- U.F.M. (Unidentified Flying Monotreme) - Some have their heads explode from Melody crying; the leader and the others crash into an asteroid and explode
- Mayor May Not - Ran over by The Mole.
- Give Me Some Space - Hit by asteroid.
- Living Daymare - Hit by Gutsy.
- SunFall - Hit by the sun.
- Disco Night - Crash into the moon (only in dream).
- Platypus Evolution - Die in a crash.
- Abduction - Die in a crash.
- Out of this World - Die in a crash.
- They made their debut appearance in Warning.
- They were chosen to be platypuses because of the platypus' odd appearance.
- The leader is probably a base on Darth Vader because of the similar-looking helmet and cape. Both also kill their own minions.
- There is a young platypus alien who doesn't have much expierence. He is usually only for lookouts.
- They are the first characters to die in Season 2.