Here is my explanation   (I like this one
 (I like this one   )
)
When you play corsair marauder, you put the card very slowly on the table. On his way, you choose a posession. Marauder is still approaching the table. Now, you discard a posession. Meanwhile, Corsair Marauder reaches the table.
Know it hits the table and it is played.
Shadowplay triggers.
I'll work this one just like the Gollum problem:
SP plays 
Corsair Marauder:
   SP Pays the cost
   Card hits the table
   SP gets to use the card's "When you play..." text first; spots another corsair and discards a weapon to add 2 tokens
   FP gets the first optional action; uses 
Shadowplay to exert the Marauder
      SP either has no response actions to the Marauder being exerted or passes 
      FP gets next optional action to the exertion; plays 
Unheeded to wound the Marauder, bringing his vitality to zero and killing him
         SP either has no response actions to the Marauder being wounded or passes
         FP gets optional action to the wound; has none, passes
   SP has no more optional actions to the Marauder having been played; passes
   FP has no more optional actions to the Marauder having been played; passes
Corsair Marauder hits discard pile
That all happens in about 1.5 seconds in a tournament folks, because most of it is implied and understood.
In the end, the Marauder does his job. End of story.