The first two enemies you'll find are Atlas and Eliot, Eliot has quite a lot of health. Smash the barrel before moving all the way to the right, where Mic will walk on. The next batch of punks are some of the weaker guys, like Schot and Mark. Once they've been defeated, some stronger Mad Gears will come on, like Atlas, Robert and Eliot.
Head right until you can go no further. There's another barrel to break open, and Leon and Atlas will also come on. Defeat them and break the barrel, and then Robert and Elias will walk on. Once they're beaten, you'll have to fight Andore and Jack. Once they've been defeated, the train will start moving off, but you'll automatically jump onto it.
On the top of the train, you'll have to fight a lot of strong enemies here, including Elick, Elias, Atlas and Andore. Move on to fight even more enemies, including Andore Jr. Watch out for the Elicks -there are several of them here.
Once you can move on, you'll find another Elick, along with Bull and Schot. Once you defeat one of these guys, watch out for the Joes, several of them will run on and throw molotov cocktails. Jony will come on if Elick and the others have ben defeated, but you can usually get him to walk into the fires. After the Joes have been defeated (or have run off), you'll jump off the top off the last carriage, and land below.
After landing, head right. The killer clown called Philippe will leap out of a container. Philippe is very fast, and is armed with a cane. He will attack with his cane, which has decent reach. He also has a very fast slide kick, which will knock you down if it hits you. However his most dangerous attack is his grab, where he'll hit you over the head repeatedly. This does a lot of damage, so try not to let him get close to you.
Once way to fight him is to keep throwing Mad Gears at him. He gets a lot of backup from his gang, but you can keep him at a distance by constantly throwing other enemies at him. Another slow but sure way to win is to keep hitting him with jumping attacks. These don't do much damage, but Philippe doesn't have much health compared to the other bosses. Once he's defeated, the train will come to a stop, and you'll automatically jump off it.