Ho-oh in Colloseum

[Chris 2.1]

I've beaten the 100 trainers in Mt Battle but haven't purified all my shadow Pokemon (I have 2 left). When I purify them, will I recieve Ho-oh, or do I need to beat the 100 trainers again?

[Poryhedron]

I don't know for certain, but I would guess you'll have to.
However, I should ask if you cleared the correct Mt. Battle. The Mt. Battle you need to clear for Ho-Oh isn't the one that's accessible in story mode.

[mr_pikachu]

I can confirm that you have to beat the game and then clear Colosseum Mode, as the team with which you clear the 100 Mt. Battle trainers must be registered from Story Mode. You can use any Pokemon you like - transferring your ace fighters from your GBA is perfectly legitimate - but the game must recognize it as a "Story Mode complete" team.

[Crazy Elf Boy]

What Mr_pikachu says is true, but make absolutely sure your pokemon are in your story mode game and not straight form the GBA. I did that once and I was not happy

[Chris 2.1]

I did beat the 'actual' MT Battle (ie facing Latias, Latios, Regi's, Kyogre, Groundon and Jirachi etc along the way) with a team from Colloseum I registered (but then did move them onto my GBA, but that is irrelevant).

The thing is though, will it give me Ho-oh after registering that I defeated Mr 100th-Battler (in which case I can just go to Area 10, I believe) or will I definitely have to start from 001 again!?

Because that would be VERY soul-eradicating.