100 player map! HOW?!

These maps are created by the system as one gets full another one is started. This is to ensure we keep as many active players as possible on a map instead of having a dozen 100 player maps that have a couple of players.

I heard that cards for 100 players are not only created by the system, but can they be created manually?

Not by players. If you get enough players signed up, a game operator might create a game for you.