First things first - the beast mode does look apesish - unlike the original BM OP. Lots of brown fur. The head's got the snarling gimmick you may have seen elsewhere. The Spark is in his left arm and activates the blast punch gimmick in both modes.
TF to Robot mode: Fold the legs out, flip the toes over. Rotate the left arm at the wrist, and the right below the elbow. Fold the Ape thumbs down, bring the wrist guards round to the front, slide the fingers through and fold them back. Pull the lower chest down & open the chest up. Fold down the ape head and close the chest. Rotate the entire chest down into the body revealing the upper robot chest and head. Fold up the lower chest & raise the shoulder pads.
You end up with a robot that looks familiar in a cartoon accurate type way, but more in OpOp's colours. Maybe a little too much translucent orange on the upper body but hey ho. Joints at the knees & hips, waist neck and shoulders. The right arm has rotational joints above and below the elbow, and a small amount of movement at the elbow. The left arm has a wrist rotational joint, but nothing between that and the shoulder - due to the punch action. Both hands have posable thumbs and the hands can either be open or closed in a fist/holding something. The head is the BM Op head - which as we all know is not a proper Op head - in mainly yellow, but with a brassy type mouth area.
The gimmick: The weapon's primed either by cranking the shoulder pad or by rotating the forearm. By my reckoning the clear orange section wants to be on the under side of the arm for the weapon to be primed correctly, and the forearm needs to have been cranked through at least 180 degrees. Then, If his left hand is positioned correctly (in either mode), the missile can be locked in place. Pressing on the Spark causes the forearm to unwind with a clicking noise and then suddenly the forearm springs forward and the missile is deployed with some force !
The toy's bigger than BM Op by a long way, and probably about the same size as TM Op, although the chest is less broard and this makes it look smaller. The robot is 15 cm high.
Yet another good late BM toy.