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As a fan of clan Skyrye I was disappointed when GW did not release any new warlock engineers and so I started thinking of how you could make one as well as a couple other plastic minis, note that these are just my ideas and if anyone has any insight or ideas of their own id love to hear them.
Warlock Engineer: for the body of the Warlock Engineer I would use the body of the plague priest from the plague furnace sprue. Very carefully trim/cut away the spikes on the shoulder and the boils on the tail, feet and hands. This will give you a fairly decent robed body. For the head I would use the drivers head from the doomwheel, I’m referring to the head that is completely covered. If you wanted to use the other that’s up to you. As far as the arms I would leave the staff in his right hand but convert his left hand to be outstretched with some sort of contraption. You can model it depending on your war gear. No Warlock Engineer would be complete without a large brass back pack and for this I would take the tank from the back of the doomwheel.
Assassin: this conversion is very simple. I would use the body of the Grey Seer from the screaming bell sprue (the base will have to be converted to work with the models unique feet positioning, I’m thinking maybe a pile of bodies) it would be assembled as normal minus the head or any other bit marking it out as a Grey Seer. The staff would need to be cut away as would the handle section which attaches the Seer to the bell itself. For the assassins weapons I would take 2 blades from the front of the doomwheel. The hand behind the body would be holding a reverse grip on the blade while the right forward facing arm would have a standard grip. The head could be taken from any suitable hooded model such as one from the clan rat sprue but I would prefer to use one from the plague monks.
Warp Grinder: I am still working out how to do this one but my idea so far is to use the co-pilot from the doomwheel as the back pack carrier in the model with the brass tank being what he carries. Replace the handle in his hand with some wiring/cable coming out of the tank. For the operator I would use the arms of a storm vermin halberdier with the blade cut off and replaced with the warpstone shocker on the side of the doomwheel and add wire/tubing connecting the butt of the weapon to the wire/tubing in the carrier’s hands. The operators’ body would be a plague monks robes with the head of a clan rat.
Hell Pit Abomination: this is the least finished of my ideas but I’m thinking of using a Vampire Counts corpse cart as a platform to hold the blind wyrm portion of the body. Giving it to front legs of some sort and the upper mutated torso. The only real idea I’ve had so far of what to use from the worms body is the body of a stegadon.
"I don't wanna kill ya, you're just too ugly to let live!".
I would use rat ogre for a start for my hell pit abomination. He has more then one head en also more then 2 arms Im going to look into some slave bits