The easiest way to get this is to play through the whole game on easy and collect everything, than replay each level on Hard with Hardcore. You will have all your skills and items and you can focus on speed running the levels. These do not need to be done in mission order.
The Skeleton bosses are very easy just use Warrior and block than jump attack.
The Goblin bosses are a pain to fight but good news, you never have to kill any! The first one i just ran past and pulled the switch, second and third can be lured off the cliff with a little timing.
If you need help finding any collectibles I found this guild great.http://gamerwalkthroughs.com/trine-enchanted-edition/astral-...