I wanna be the Diverse
Once the 2 paths are beat, you get access to one of the most iconic VVVVVV stages in any fangame. It culminates in an epic multiphase boss fight against Vridian and Vermillion that you will never forget.
A final path opens up that has some fairly tricky platforming at times, and a lot of traps mixed in. At the end you are rewarded with 2 more boss fights, the final one again being very memorable.
This is one of the old iconic fangames that everyone should really play.
Production Value: 9/10
This is one of those games that starts out looking bad, but it is a fantastic game. Some areas include a Mega man 3 stage, Sonic advance stage (springs) and an astonishingly well put together VVV stage. The final stage was the only one I didn't enjoy too much because it is mostly difficult spike jumps and traps, similar to that of I wanna be the Crimson.
This game really shines through with its bosses. They are absolutely top-notch, 10/10 bosses. I wouldn't change a single one. The final boss, Ultimate Luigi, was the best one of them all. I also love the music chosen for the bosses. There is also a crazy mouse-shaking effect in the VVV boss which freaked me out a bit.
Give this game a play if you haven't already.
The bosses are the definitive peak of this entire game; all of them are very great. Especially the last 2 ones blew my mind. It starts out bad but later on you'll realize that this is not a generic fangame.