Dimensional Prison
Trial: Finish the level after defeating the Forgotten One after absorbing 100 Neutral Orbs during the fight against him
What you want to do is start off with a Guillotine to get your focus meter up instantly, the you want to retreat as he likely follows up with a slam move up close. At this point you want to get in close after dodging his attacks and hitting him as much as possible. I typically retreat and grab the orbs on the next attack. You are not going to collect 100 orbs before activating the start of the second phase. What you want to do here is just deflect the attack and let him recover. I did this until I had 13 left then entered phase 2. That gave me a checkpoint to get 13 Orbs. Second Phase is bit harder than the first as the weak point is no longer at ground level. Do not attack from the air. Always use the Guillotine from now on until the end of the fight.
The Underworld
Trial: Finish the level after destroying all 16 Flaming Skeleton Warriors.
So you will be fighting 4 waves of 4 Skeletons. These guys are no different from the regular skeletons so use the same strategy. Counter attack their moves for heavy damage. Once they fall to the ground finish them off. Dont forget a Dark Crystal can clear a wave for you.