From the Malifaux Tactica Wiki:
A powerful model that uses Burning Tokens to power its spells, abilities and attacks. It can be the heavy hitter many crews lack, and even though expensive, you are getting a massive piece for only 9 (or 10) SS.
The Rail Golem works well with models that can put Burning Tokens on it, but it is self sufficient enough to work with any crew.
The Rail Golem has very significant offensive abilities. Its melee weapon has a good reach, is Paired, and causes grievous damage, and it can use Burning Tokens to get positive twists to attack or damage, or an extra melee attack.
The main "trick" with the Rail Golem is to balance out how it accumulates and uses Burning Tokens. Often, you will need to balance between increasing attacks in a short-term way (by increasing attacks and damage flips, or getting an extra attack), healing up (by burning all tokens for 1 Wd of healing each), or saving them up to Reactivate (which costs 5 tokens, but can be very powerful.)