I used this speedrun to help me beat the game on hard & plan to use it on extreme as well.
A couple of things to note... 1. He's using hard pogo, but I used easy & was fine...
2. He uses a glitch trick to skip some rocks in the Mine & the door blocking the Moon
(because he's speedrunning the game)I've found that on the Xbox 360 version it DOES work, but the rocks respawn... Because there are several you have to glitch away in the Mine stage, I can NOT get it to work
(but it might still be possible), but Because there is only 1 on the Moon it worked
easily.3. He does not get the 5th heart container because it was too far out of the way, but even without it I was able to beat the game on hard because on the last stage there are SO MANY ice cream cones it's hard not to be at full before the boss fight.
4. The suicide strats he uses are fine to use on Hard mode because you have infinite continues, but I do NOT plan to use them on my extreme run.
Video credit to AGDQ & Satoryu links to both their official pages can be found on the video.