Warhammer: Vermintide 2

This achievement must be done in Legendary difficulty.

As of March 10th, 2019 the bridge collapse method still works! If you find your group doesn't have enough firepower to down the troll in 15 seconds, you can bypass killing the troll yourself and still get the achievement using the following method.

First the roles:

One player is designated the Bell Ringer, and has the fun initial task of holding off the mobs in the end sequence until everyone is in position, and needs to move quickly onto the bridge once the bell is rung (so someone with a dash is ideal for this position). As such, we used a Foot Knight for this role. No ammo is needed for this role, and a strength potion is nice but not necessary (for clearing out mobs before ringing the bell). Speed is also useful for someone without a dash ability.

One player is designated the Troll Agro-er, and positions themselves on the bridge near the doors that the troll enters when the bell rings. We had a Shade in this role (because a Shade dies quickly when undefended). This position needs enough ammo to get the troll's attention. No potion is needed.

Two players are designated Level Completers, and they go as far past the troll doors as possible, positioning themselves right by the wooden barricades that break when the troll dies (its off to the left and up a hill a bit, aka the furthest in the level you can possible go before the troll sequence). In a best case scenario, you want lots of ammo for these people. Speed potions are helpful for these people to get into position quickly, but not necessary. Really, any class can do this role, but ranged damagers are slightly preferred.

Now what to do:

1.) Once the party reaches the bell, the party clears out all current specials and dangerous mobs (they'll continue to spawn, but at least we'll get the worst out of the way for the Bell Ringer). During this time, it helps if the Troll Agro-er and Bell Ringer take some damage so that they're not at full health (helps later when the troll needs to kill them), but be careful as to not take too much so that the Bell Ringer drops before everyone can get into position.

2.) During a lull in fighting, the Troll Agro-er and the Level Completers move into the positions detailed above. NOTE: the Level Completers will see bits of the level collapsing as they approach the wooden barrier that blocks them from completing the level. This is good, and indicates that the trick will hopefully still work.

3.) The Bell Ringer clears out as many mobs as they can, waiting for another lull in fighting. The Troll Agro-er can assist from range if they have enough ammo (make sure you still have plenty for the troll). The Level Completers should heavily assist from range as they should have a clear path to shoot the mobs from up above. MAKE SURE TO KILL ANY MOBS THAT CAN MOVE OR DISABLE YOU, especially halestormers, hookrats, etc.

4.) THE BIG SEQUENCE BEGINS! Once the coast is relatively clear, the Bell Ringer rings the bell (starting your 15 second window), and immediately runs to where the Troll Agro-er is at mid-bridge.

5.) The troll, upon exiting the doors, will want to cut immediately right and head up to the people by the exit. The Troll Agro-er needs to shoot the troll at range and get his attention before the troll does this. If successful, the troll should charge onto the bridge.

6.) Once the troll gets onto the bridge, you want it to walk to the center to ensure it dies when the bridge collapses, so bait it to the center. NOTE: Once its there, make sure to stand between the troll and the railings of the bridge, to prevent the troll from punting you off the bridge.

7.) Let the troll kill everyone on the bridge as fast as possible. In Legend, he should do this really fast (hence, why a Shade was a good choice for the Agro-er, as the Shade dies fast undefended). You can also speed this process up by range attacking each other. Don't use bombs though, as this will stun the troll.

Once the two people on the bridge die, the bridge will collapse (due to the Level Completers being far enough away that the game glitches, thinking the troll is defeated and the level can be continued). If the troll is in the center of the bridge, it will drop into the chasm and immediately die. Achievement should trigger immediately if done within 15 seconds.

Don't forget to finish the level! You'll need a completed level with achievement to work toward the Empire Resurgent achievement. The good news is that the Level Completers have a straight shot to the exit with no mobs in the way, Congrats on completing a extremely tricky achievement!