Duke will encounter this boss at the bottom of Morphix's G.L.O.P.P. tanker; the area the battle takes place in is quite small. As soon as Duke jumps down into the section, the boss will be there waiting for him. Like the other two variants, it spits out three G.L.O.P.P blobs that do 20 damage each if they hit the player; in addition whether the shots hit the player or not, they will temporarily leave a puddle of G.L.O.P.P. Each puddle will also do 20 damage if the player walks on them.
To all intents and purposes, it is identical to the Level 2 variant; the only real difference being its much higher health. During the battle the player can expect to sometimes have to aim up to hit the boss. Fast firing weapons such as the Assault Rifle work best for this. The player just needs to be careful to avoid its attacks and jump over the G.L.O.P.P puddles when necessary because as it's a boss battle, they would want to take as little damage as possible. Interestingly when this boss is hit for some reason it will sometimes temporarily become invisible, but that won't stop it from taking damage. Like the standard variants he has no close combat attacks.
The battle itself has a time limit. If the player takes a while to kill the boss, the tanker will start shaking. In addition, as the battle drags on, the middle section of the floor where the player is will break open which will let them go into the lower section where they can get two ego health +100 packs and ammo. Later on in the battle, water will start pouring into the tanker if they take too long to defeat the boss; Duke will only be able to survive in it for so long before drowning and because of this it's best to get rid of him as soon as possible.