The move was made to prevent spoilers from leaked versions of the long-awaited sequel.
Excerpts of the game, which allows users to fight alongside Disney characters, have already been leaked online.
Once installed and completed, the game automatically downloads the epilogue.
"It's definitely an unusual move. It is the first time I've heard of a game doing this," said Caspar Stewart, media analyst at research company Enders.
The game, which was first announced at the E3 conference in 2013, has been a long time in the making.