Epic Mickey 2: The Power of Two

To befriend an enemy you simply need to use Paint instead of Thinner. Doing so will cause enemies to stop being hostile and will be shown to have blue mickey heads coming from them. If you paint all enemies you will unlock this without trying well before the final boss. It should be noted here that you can't paint Beetleworx enemies. Spatters are fair game and Blotworx must have their red buttons jumped on to expose their pilots which you can then paint and make friendly.