Would the critical allowed by marksmanship set off the harpoon missiles effect. I am not sure if the card is received before or after the critical is assigned or if it makes a difference. Thanks.

Harpooned! is assigned after you make the attack, so Marksmanship would not trigger if the defender does not already have Harpooned! . If they do, then yes, it would trigger.

Very nasty with Jostero.

All damage is resolved before the condition is assigned, so no. You can't set off the condition with the attack that assigns it, Marksmanship or not.

Thanks, thats what I thought, but wanted to make sure.