Best/favourite 100% completion reward?

[Swamperon]

I'm always appreciative of when a game gives you an extra special reward for achieving 100% completion (or it's version of that) of it. Was wondering what other people considered some game's best 100% rewards?

The best one I can think of is Sonic Adventure 2's 3D remake of Greenhill for getting 180 emblems. It's extremely frustrating thing to do but playing through the first ever Sonic level in glorious 3D made it worth it.

On the other hand, when a game offers only a harder mode as a reward it usually bores me. Few games are worth the effort of another playthrough after already beating the original 100%, though there are exceptions.

[Tempest]

I'm always appreciative of when a game gives
On the other hand, when a game offers only a harder mode as a reward it usually bores me. Few games are worth the effort of another playthrough after already beating the original 100%, though there are exceptions.
I can think of only one game where I cared/liked it enough to try hard mode and that was Gitaroo Man. I never could beat the last level on hard (master). Every other game I felt like "Oh wow my reward for slogging through this game is to slog through the exact same game only with slightly harder enemies and more damage. Woo hoo!"

Tempest

[TonyTheTiger]

I remember Magic Knight Rayearth had neat bonuses for collecting all the rainbow amulets. It unlocks a collection of outtakes from the recording sessions.

Super Mario 64 offered up some fun thanks to the cannon that opens up when you get 150 stars, too. Some of the fun was due to completely unintentional glitches.

And Castlevania: SOTN actually made completing the game necessary to get the best ending.

[Nophix]

A near naked Samus Aran.