The twofinity train is a twofinitely-long train that captures children and forces them to undergo character development. In charge of the twofinity train is the authoritarian, insane conductor, Two-two, and his army of heralds.
The twofinity train was constructed following a catastrophe of universal proportions that lead to the external universe being uninhabitable. The only life in the world of the twofinity train as it constantly circumnavigates its cosmos is inside the twofinity train. The goal of the twofinity train is to force the children it captures to undergo character development so that, come the day that the external universe is habitable, they will be fit to rule.
Each child captured by the train has a Number, a representation of how far they are from the personality type dictated by the train (INTJ). Getting this Number to zero allows the child to leave the train and enter the next stage of the challenge, the World Trial.
The twofinity train is made of an assemblage of cars, each built by Two-two in the Engine room. Each car contains a Trial, which must be performed to decrease the Number of the person doing the Trial.