No, they do not.
The main reason being because the platypus is native to Australia. And there are no tigers native to Australia.
However if tigers were native to Australia, it is likely they would hunt and eat platypuses if they were very hungry. To a tiger, the platypus wouldn't be very filling, so they would prefer larger prey, like a kangaroo.
No. If they could find one they probably would eat them but there are no tigers in Australia (outside of Zoos) and no Platypuses in Asia (outside of Zoos).
No. Platypuses do not eat mangroves or any other plant matter.
Platypuses do not eat earthworms or other terrestrial worms. They eat aquatic annelid worms.
No. Platypuses eat small water animals such as aquatic insect larvae, fresh water shrimp, annelid worms, yabbies and crayfish. They do not eat anything terrestrial.
No. Cougars do not eat platypuses, for the simple reason that platypuses and cougars occupy different continents. Platypuses are endemic to Australia, and there are no cougars in Australia.
No whales eat fish
Probably the largest thing which platypuses eat are small yabbies, which are a type of freshwater crayfish.
Platypuses do not eat plankton, so they do not need to find it.
Platypuses do not eat land food. They feed entirely off crustaceans and small water creatures.
No. Platypuses do not eat grass or any other vegetation. They are carnivorous, feeding only on small aquatic invertebrates.
Platypuses do not have teeth, but hard bony plates which they use to grind the food.
As there is no such thing as a purple platypus, this question is impossible to answer. Platypuses eat crustaceans and larvae that live on the bottom of creek and river beds.
Platypuses are not cannibalistic. They do not eat their own kind.