This isn't too bad; I just had a quick go on the DLC tonight for 30 mins and no plan of attack and after 4 tries I got it. It does require a certain technique though; at least for speed and ease.
By far the easiest mission will be The UAC, as it is by far the shortest. This method will bag you 650,000 points (requirement for Gold on I'm Too Young to Die is 600,000)
Just Play on I'm Too Young to Die. The Bronze, Silver and Gold are earnable on all difficulties and it seems that they naturally all go up depending on difficulty, as you get more XP for each difficulty. Play on the easiest mode for the easiest time (obviously)
1) Time, at least for me, was not really a factor. I consistently did it within 7-8 minutes and got Gold twice, and I would say for the method I propose under 10 minutes is pretty easy. So don't worry about time too much.
2) Two Extra Live Pick Ups (they doom dolls like the collectibles in the base campaign) are available. PICK BOTH UP. You get 50,000 points for each one = 100,000 in total. Although they give you extra lives, on easy you will come nowhere close to dying even if you're new to DOOM. Thus, Death is not really a concern with this achievement.
I would be very surprised if you DIDNT find them. As I said, time isn't a factor, and map isn't confusing. Both are after the blue key card. They should be easy if you explore enough
3) The other new feature are Mine / Bomb like items which appear in the air. When shot, they shoot out a relic, which gives you a gold pickup worth 50,000 points for when you pick it up (just run into it). There are 6 in this mission. You Will need to shoot all 6 mines, and pick up the flying relic AS SOON AS POSSIBLE (within approx. 5 seconds.) Otherwise this will turn into a silver pickup worth 40,000 points, and even a bronze. Every point matters. If you miss a gold relic, restart. All 6 will bag you a whopping 300,000 points.
I would be very surprised if you DIDNT find them. As I said, time isn't a factor, and map isn't confusing. 1 is in the first area with enemies (can't miss it) and the others are after the blue key card. They should be easy if you explore enough
4) Keep your chain multiplied as much as possible. I failed on my first few attempts because my multiplier was on 4x for a lot of the mission. You're going to want to maintain 16x (and occasionally 32x) multipliers for the remaining 200,000 we need. My main bit of advice is as follows
- USE GRENADES. Explosion kills add so much to your multiplier, and by killing enemies you seem to pick up grenades almost as fast as you use them. Spam grenades, especially is your multiplier is about to drop.
- Shotgun and Glory Kill Combos are also a good way of dispatching enemies. Your shotgun ammo might drop to 4-5 at times, but as long as you pick up ammo and kill enemies with ease you should be fine for bullets.
- The first area is actually the hardest. After the blue key card, you will not have your multiplier reduced by damage barely at all, but the first area has lots of imps (the dudes that shoot fire at you). Watch out for these, as they will break your multipliers with distance shots. Take them out with grenades and shotgun bullets quickly. You're going to want to keep your multiplier up in this area, and by watching out from these imps I went from finishing to get the blue key card from 62,000 to about 75,000.
That's pretty much it; load it up The UAC on the easiest difficulty, collect all relics and extra life dolls and use grenades, shotgun / glory kills to keep a combo at 16x and 32x as much as possible. 600,000 is the goal.
Thanks guys! (Will update with relic and life doll locations soon, but for now they aren't hard to find at all)