This is a guide to help take down Slag.
Tools of Destruction
Slag serves as a boss in Tools of Destruction. In the first part of the fight, Slag attacks by firing blue crescent-shaped missiles at Ratchet and swiping his claws if the Lombax wanders too close. The missiles can be destroyed by any weapon. Ratchet must simply avoid Slag's attacks while damaging him with his weapons (preferably with the Nitro Reaper, Toxic Swarmers, Doom Blades, or the Judicator). After enough damage, Slag will jump to the top of the ship and summon his pirates to attack Ratchet. Destroy them to force Slag back down.
Now Slag gains a new attack: turning his hook into a hammer and slamming the ground to create a large shockwave. Slag will alternate between these two weapons, making the battle somewhat difficult. Like before, dodge Slag's attacks and use your strongest weapons until he jumps back to the top of the ship and summons more pirates to attack.
In the final round of this battle, Slag now attacks by turning his hand into a grog mug, allowing him to literally belch out streams of fire. Slag now switches between these three weapons, as well as using his claw swipe. When his health is critical, he'll jump back to the top of the and summon more pirates. Destroy those pirates, then finish off Slag.
Quest For Booty
Slag makes his return as the final boss of the game. The fight with him takes place in the Azorean Sea on his fleet. There are four parts to this battle with him. The main thing to remember is that Slag and Darkwater are sharing the body, meaning you will have to contend with both of them.
Slag opens the fight by firing his blaster at Ratchet. The Predator Launcher is great for dealing damage, and the Nano Swarmers are great for keeping the pressure on Slag. Slag will also move in to swing his sword at Ratchet, and may stab the ground, creating a shockwave (the sword will get stuck in the ground, leaving him open to more attacks). After enough damage, Slag'll teleport to another ship in the fleet.
In this round, you will be treated to a nasty surprise: Darkwater will take control of Slag, transforming into a giant, green ghostly version of himself. Darkwater attacks by slamming his swords on the ground, creating green shockwaves of energy, and occasionally summoning undead pirates. Darkwater is also immune to all weapon damage save one: objects marked by death. First, kill the undead pirates, then grab the skulls they leave behind and throw them at Darkwater. This will release his hold on Slag. Now you can attack Slag until he teleports to another part of the fleet.
This round is relatively short, and there is not a lot of room to move and dodge Slag's sword attacks. Slag attacks with his sword and blaster. Like before, use the Nano Swarmers, Predator Launcher, or the Magma Combustor to damage him until he teleports one last time.
This is it, the final round. Slag and Darkwater are at the end of their ropes, and its up to you to finish them both once and for all. This round is the same as the previous three, except that Darkwater will take control more frequently, and that it will take more than one pirate skull to break his grip. Otherwise, keep pelting Slag with your strongest weapons until you take him and Darkwater down for the count.