For trophy and other information, try http://www.dojo.com/blog/witch-hunt-gameplay-tips-and-information-work-in-p-25
I've spent way more time on this game today than I should have; finally got stuck on Level 7 of Stage 3. So close to the end ...
Although the "featured recommendation" on the game page about sticking to only ice as a strategy has been shot down fairly well, I still kind of prefer ice overall. Maybe I'll try a fire strategy when I come back since ice seems to have gotten stuck at this level.
Even if you've got the soccer penguin and the reaper out, ice is too slow to be effective by itself. I usually use the fire penguin and then alternate between ice and lightning.
The all ice strategy works rather well for the last set of stages. Keep ice pengu and collector running at all times, and use the rest of arcana for ice freeze(ice power #3) against freeze-resistant enemies(the purple hulks and the shield bearers). It may help to call thunder and fire to wipe those two enemies out(thunder can shatter the shields, fire roasts the purple guys), but it's not really needed, and it's not nearly as fun as playing collector spam.
Of course, you'll need a different strategy for survival... and make sure that you're getting your share of kills, as you'll need 10k.
just finished all the quests, vanisher trophy is very boring
some tips in the endless mode:
freezing down flying enemies help. ALOT
toggle between ice and lighting if there is no fliers to take down
bosses give a lot of gold
arcana 2 from lighting is very good too
always have fire and ice penguins on
try to aim the ice from an angle that will hit a lot of monsters
arcana 2 from fire can be used often too