Metal Gear Solid V: The Phantom Pain has a normal ending, and a "True" ending. Seen above, in order to view the True ending and earn some exclusive items you will need to do the following:
Complete all important (yellow tagged) Side Ops including #150.
Upgrade all Mother Base facilities to level 5.
While completion of main story missions and facility upgrades will come naturally as you progress through the game, unlocking Side Ops #150 is a bit more complex in nature. In order to unlock Side Ops #150, you will need to do the following:
Get Quiet to level 10 Bonding (highest level). This can be done by completing Side Ops with Quiet as your Buddy.
Never use the Butterfly emblem design. Using this design allows you to continue using Quiet as a buddy after she departs during Mission 45. She needs to leave in order for you to unlock Episode 46.
Do not kill Quiet during Mission 11. When provided the option after your skirmish, you need to avoid pulling the trigger.
Once you have completed Mission 45 and Side Ops 150, Mission 46 should unlock. Completion of this mission will reward you with the true ending, a Leather Jacket uniform, and Infinity Bandana.
