I love trophies (or achievements, whichever your poison)  
 
And i aim to complete ever game i get to it's fullest (ridiculous investment onlines for dead games, and unfair multiple playthroughs are my exceptions) 
 I have finished Vanquish in it's entirety, found every collectible, finished without dying - jumped through every hoop they have asked me - the works... 
 
BUT 
 
There is one thing remaining, one sole trophy left to achieve before my platinum is awarded, it's for finishing all the challenges, there were 5 of them. 
I set to work 
It was hard, waves upon waves of very difficult enemies, with no checkpoints between waves, making death extra punishing. 
I persevered 
Challenge 4 gave me the most trouble - It kicked my ass for 3 days straight 
I crushed it in the end. 
Challenge 5 was barely worth a mention compared to 4 - i cleared it out in a few minutes. 
 
Then challenge 6 unlocked - i was not aware it existed and was a little upset that my victory had been postponed by this late contender. Nevertheless i licked my lips and prepared to floor this game one last time to claim my prize. 
Hell, after challenge 4 - nothing can be a task anymore right? 
 
Wrong  
 
Challenge 6 is too much for me, it takes so damn long, it's ridiculous - the slightest error at any one moment leads to death - the enemies are relentless, I've only made it through to the final wave once and i lasted approx. 20 seconds. 
 I can't quit now, not this far into my 100% mission, this last feat is all that stands in my way - but i'm at my wits end. 
 
I've looked online , even browsed youtube videos on how the pros have cleared it out - it takes the quickest ive seen about 15 minutes to finish, and even then he rides his luck at times that you just can not emulate. 
  
  

Unfortunately I cannot offer any advice, however for having all the other achievements/trophies in that game I salute you.
 
I just finished the game today and even on normal it was difficult at times.  I want to play through it again on the harder difficulty settings and at some point clear the challenge levels, but I think it's possibly beyond me.
 
All I can say is good luck and I hope you get that platinum!  =D