Someone just find a solution (apparentely) about those 2 unobtainable achievements in Dark Void GFWL: Fireworks and Demolition Derby.
, and for everyone that doesn't want to go there, here's the whole post about it.
Dark Void is 100% possible to get all achievements on GFWL. I know as I did it after 8 long hard months! This is what you need to be aware of:
1; There appears to be a nasty bug so that after a certain number of LIVE Guide button presses (20 to 30 maybe more)the Games On Demand version loses the GFWL interface which is apparent when you hit the Guide button & nothing happens! obviously this means you cannot earn achievements so the game appears to stop tracking the stats towards the achievement as the data is going nowhere. Restarting the game to get the GFWL interface back makes no difference it does not remember your offline progress so you have to reload the chapter again up to your last checkpoint saved with GFWL interface active.
I found out the hard way when trying to get the Journals achievement that took me forever as some levels contain the journals so well hidden without an online guide you will never ever in a million years find them they are in the most pathetic place you could possibly imagine ingame & several do not even appear onscreen until you are within a few metres of them its very badly implemented. Be aware anytime you lose connection to GFWL either through the bug I found or your connection drops for some other reason you lose the progress of collecting the journal unless you reached an ingame checkpoint. This is mega frustrating as some journals require an epic journey/battle to reach them so you have to scrap all that progress & start again....... Find a decent map online & youtube videos but even then you will be amazed with how hard some journals are to find!!!!
2: For the grenade based achievements you have to Cook them by holding down the button & timing it so the grenade explodes above the head of the Knight for the Big Bang Achievement. You have several different colour grenade types ingame & some only appear in certain levels. For the Blue Light Special Achievement you must Cook an Alien (Blue grenade). This is tricky as the blue grenade is rare & having to time it so it cooks & is thrown & explodes killing 3 enemies at once takes a lot of gamer skill! Some also require you to cook the grenade so it explodes over the head of the enemy which is tricky to time correctly..............
3: For the achievement Demolition Derby this is another very glitched achievement & the only reason I got this was by complete fluke. I spent 8 months replaying Chapter 4 as there are a few UFO sections in those levels. Colliding is hard enough anyway but as the GFWL interface disappears on its own you can lose any progress you made with collisions as it does not count them so unless you collide 10 times whilst connected to GFWL or you reach an ingame checkpoint & are still connected to GFWL you lose all progress up to your last checkpoint connected to GFWL. I remember how this popped for me I had been playing for a while & still had the GFWL interface present then I exited a UFO as it was crashing & threw a cooked grenade which hit the UFO chasing as I was on the side of a rock with a big drop below! It was total fluke but it popped after a delay of a few seconds.
4: For the Fireworks achievement you must cook a grenade to explode above the head of the flying enemy so that is another very tricky achievement to get & cannot remember but your grenade may have to be Blue Alien grenades (which are very rare ingame to find so you have to find somwhere ingame where you can get Blue grenades then find a spot to Cook them so they explode above the enemy head. It seems to count UFOs or ground based enemies but this is a tricky achievement.
You need a lot of willpower/luck to max this out due to the lack of QA by Airtight games the GFWL interface goes missing which is why so many have had problems with achievements being unlocked offline only then not syncing to the Online GFWL profile when you reconnect to GFWL.
As long as you keep checking every few mins ingame that the GFWL interface is there & reach a checkpoint all achievements are possible. For those grenade based achievements remember to cook the grenade before throwing it & the different grenade types Blue especially. If the GFWL interface goes missing just exit the game & restart it from the desktop but you will only have progress up to the last checkpoint made until GFWL went missing.
I spent probably 100 hours trying this over 8 months so its a grind but doable if you have the extreme willpower as several of the journals are right at the end of the level & you can find the GFWL interface has gone missing before you can reach the checkpoint so you have to backtrack from the last checkpoint which is really gamepad throwing against walls frustrating.......