Sling has the trap mode common to each of the first 4 original Neo dinosaurs. Simply split his fin in 2 down the middle and fold each half to the side. Inside there's a yellow and red flowerlike pattern and a knob at the centre. Press the knob and the entire thing springs closed venus flytrap/man trap style. Nice.
TF: Pull the spine away from the back and the back away from the underside of the body. Fold the spines to your right and the back to your left, swinging the forelegs under the body. Turn the robot legs round at the robot's waist 180 degrees, turn the beast head round 180 degrees and fold down onto the chest. Fold the root head up from inside the chest cavity, lock in place and spin it round. Cover gaping hole in the back by moving the forelegs round. Fold beast tail up onto one of his arms and open the fan as a shield on the other.
The resulting robot is very thin and very orange with Dimetrodon pieces hanging off the arms and chest. His helmeted head looks similar to Terrorsaur with a crest down the middle. On his right arm is his tail which I assume is meant to be a gun or a sword, on his left is he sail forming a shield. The beast head covers a pink/purple Destron (Predacon) spark crystal, and if you look inside the back of Sling you can see how it works - a metal disc covered by clear plastic which distorts the shape of the hole in the metal to form the faction symbol. Ball joints abound on this toy as was the norm at the time - they are after all the easiest way to get a large range of motion. Ankles, knees, hips, waist, neck, shoulders and elbows. The fists have a very small peg hole (2mm tops !)
Overall: Not the worst basic in the world by any means, but it doesn't set my world on fire. I think the vast expanse of orange isn't helping, it's very plasticy and an odd colour.
Sludge was sold in a 2 pack with Snarl.