The Expansion Pack for Fzzzt adds material for a 5th and a 6th player and 8 cards for the conveyor belt deck.

So the exansions consists of:
4 starting cards for the 5th player
4 starting cards for the 6th player
8 conveyor belt deck cards: 2 production units, 1 Fzzzt, 1 robot upgrade, 4 robot cards

In a 5-6 player game there are only 4 auction rounds instead of 5
(12 cards in the conveyor belt rather than 8 in the standard game)
In a 2-4 player game one can choose a longer game (6 auction rounds instead of 5) by adding the 8 additional cards to the conveyor belt deck.

There are no important changes in the rules.

The cards in the expansion pack are the same size as those of the second, tin box, edition of the base game, which is different from the size of the first edition.