The Marvel Trading Card Game was sold separately that let you play against the computer but it was meant to teach people about the game so they would buy boosters and play online. The bad news is that the online part of the game doesn’t seem to be catching on. The good news is that they are releasing all the cards, so players can build any deck that they want to. Presumably the online part of the game will go down in a few months, but until it does, you can play against other people for free!!!
Main Webpage for Marvel TCG
Download the Windows Client
The Marvel TCG has some of the older Marvel cards from the VS TCG.
The total number of cards is 852 and includes the following sets:
Marvel Origins (released April 2004)
Web of Spider-Man (released September 2004)
Marvel Knights (released February 2005)
The Avengers (released August 2005)
28 cards from the Fantastic Four starter set.