Here is my explanation (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.