Probably the first thing I've done that could be described as a pugbash is starting to turn a (very battered) GWR body, a Dowlais chassis, and a Hornby troublesome truck into a tender-tank.
The first steps were cutting the cylinders and rear buffers off of the loco before fitting it to the chassis. The coupling hook was then removed from the rear of the loco, and the already damaged coupling on one end of the truck (to use the Sudrian term) cut off completely.
The next step was to couple the vehicles. This was done using a small strip of 1mm diameter wire, which will be painted a dark colour at a later stage. The wire was bent to form a loop around the tension lock coupling bar on the rear of the loco. The tender can be attached by connecting the wire loop to the (previously cosmetic) hook moulded onto the front of the wagon. So far, this has worked in both directions light engine and hauling a pair of Mainline/Bachmann (they were second hand unboxed so I don't know which) Mk1 suburbans.
The next big jobs are painting the wire loop and making the tender look less like a troublesome truck.