Oh, so I've added the invasions to the BossType enum too for some reason... I thought there's also a pirate boss and you want to add this one ;). I have just no idea of the 1.2 content yet.

Well I remember why I've added the invasions to the BossType enum, it was meant to list everything that's "summonable" by using an item. I guess I should rename "BossType" to something like "SummonableMobTypes" later.

As for the value, it depends on what is sent over the network as the item to summon a pirate army is used, I guess it will be -3, but who knows. If you can't figure it out on your own, just leave it to -3.