I also beat the demonic mode, in about 3 sittings cause it is rather frustrating, but anyways, the game says it's 89% done. For several of the levels, I beat it 98 - 99%, cause you have to defeat every enemy and there are about 120 / level or more.. and collect all the orbs, and there are roughly 10,000 / level.. or more. (or less, depending on the level).
Yeah, you basically have to play each level perfectly to get 100%. The hard part isn't completing the levels, but figuring out how to work around the limitations the game imposes on you.
For each, you have to:
1. Get the highest multiplier possible (666).
2. Defeat all enemies.
3. Complete the multiplier challenge.
4. Collect all orbs (includes seeking them out and earning high orb counts from enemies).
Unfortunately, several things work against you for each of these:
1. Enemies aren't always plentiful enough to pull off the highest multipliers. Even worse, taking just a few seconds too long in between attacks can cause the multiplier to reset. You basically have to move the enemies around like cattle in order to create opportunities for multipliers.
2. Hellcycle levels can be difficult to reach a high multiplier, since enemies automatically stop the speed multiplier. In addition to this, chain attacks are required for earning higher orb counts. Unfortunately, enemies in the later (Carnival) levels will simply speed off if you don't dispatch them quick enough.
3. Defeating all enemies requires a thorough search of each level- which can often include a leap of faith to find enemies hiding on lower ledges.
Naturally, after doing all of this you unlock...an art gallery! It's so frustratingly old-school in both execution and reward, you can't help but laugh.
