In September 2007 the first of many Thomas-series Plarail train packs was released featuring Percy, Rocky, and two action freight cars as the Percy and Pounding Wagons Set (パーシーとどきどき貨車セット). This pack was marketed as a companion to the Thomas the Tank Engine Doki Doki Mountain Set.
The packaging for this set shows the older style of painted face Percy, but it seems that production changed to the separate grey plastic face before this pack's release, with this August 2007 production example already having the plastic face.
The plastic-face Percy, which was first developed in 2006 and reached wider use in 2007.
The two trucks in this pack have action features activated as they roll. The truck with bricks has wheels offset on the axles so that it rocks back and forth and the boxes in the blue truck move up and down as it rolls.
This was the first Plarail release of Rocky, who has a lifting boom arm, rotating cab, and flip-out stabilizers. The individual European Motor Road & Rail release of Rocky is motorized and has an operating magnetic crane but this release includes only the magnet (removed from later Japanese releases) and also lacks a rear coupling.
Rocky is nicely detailed, and his pistons can still be moved (on the European version, the motor also spins the pistons).
This is a nice pack, but I think it would have been better with the surprised Percy face already used in the Thomas the Tank Engine and Percy and the Dragon Set, and later on this Percy face was released with Rocky in a standard box.