I think for a replayability factor for Deception you would unlock specific things in all different types of modes for the game.

For instance, the Alternate Outfits should be unlocked in Arcade mode along with the character's endings.

Alternative outfits for returning characters featured in more than one Mortal Kombat game.

For each difficulty you would unlock different alternate outfits. Beating the game on easy would enable you to have returning character's Deadly Alliance outfits or for the new characters another alternate color.

Beating the game on normal would enable you to unlock character's brand new alternate outfits character.

Beating the game on hard hard would let you unlock returning characters Mortal Kombat II or III outfits depending on the character.

Beating the the max difficulty would enable you to unlock each character's classic outfits, the ones they first worn when they entered a Mortal Kombat game.

For the new characters or, characters that were not seen in alot of Mortal Kombats, they would get brand new outfits along with new alternate colors for their outfits.