Plunderlings Series 2 offered Hatchlings again (in two-packs, rather than individually, which is why I personally didn't get any), but there were a few other extras, as well. For instance, the Boom Crate.
Hit the deck! If you want to take on the biggest battles in all the sea you'll need the baddest demolitions. For the cannoneers and explosives enthusiasts in your crew, a variety of ammo is a must.
The Boom Crate is an accessory set compatible with Captain BlacJak's cannon (plus a couple other figures' smaller versions). A cannon without any ammo is just a very inconvenient soup bowl, so the Boom Crate gives us a few options for the weapon to launch: a gray stone, carved into perfect roundness; a black bowling ball with three shallow finger holes molded into it; a brown coconut with also three shallow finger holes molded into it, but additionally a "hairy" texture the bowling ball didn't have; and a dark grey mace head with smaller gray spikes all over it. They absolutely could have gotten away with making the bowling ball 
and the coconut the same mold in different colors, so the fact they didn't shows great dedication.
Each projectile is larger than the opening of the cannon, because being visually pleasing is more important than perfect logic. The set includes an adapter made from translucent plastic that fits into the mouth of the cannon and features a big balljoint the balls can plug onto.
And for a more dynamic look, there's a second "explosion" adapter that features a plume of flame and an expanding cloud of smoke, again with a balljoint so it looks like the cannon has just been fired and the ball is shooting away. And boy oh boy, does it look impressive in action! This is nearly a must-have add-on for the captain to have.
The socket in the cannonballs is the same size as the heads on all three Plunderspecies, so you know what that means: you can replace anyone's head with a cannonball, like it just fell on them in a cartoon! 
But more than that, it means the heads can go on the adapters, leading to the real reason I bought the Series 2 releases I did: you can have Captain BlacJak, holding his giant cannon, and having 8-Ball either tucked securely inside or being fired at the enemy. So much fun!
There's also a "Muscle Crate" available, which includes more Plunderstrong hands: fists, "pinching" (to use smaller figures' accessories), or open gripping hands which have a magnet inside so they can palm one of the cannonballs... or lift other Plunderlings by the head.
