Here is the full list of all 21 Rogue Rails achievements.
Defeat the Mighty Pharhord
Defeat the Frozen Killing Machine Ice-Cycle
Defeat the Creepy Spider Bot
Defeat the Cost Efficient Factory
Defeat Mushvroom, as in beating him, not like taking his feet, that would be messed up dude
Save up 1,000 coins
Save up 10,000 coins
Save up 100,000 coins
Get your first treasure
Unlock every entry in the Railpedia
Complete Adventure Mode with The Adventurer
Complete Adventure Mode with The DJ
Complete Adventure Mode with The Knight
Complete Adventure Mode with The Princess
Complete Adventure Mode with The Thief
Complete Adventure Mode with The Ninja
Complete Adventure Mode with every character