I think the mission "Built to Destroy" has some performance issues. Specifically the first two levels of the mission.

In general, the first two levels are somewhat unbearably laggy and pretty much the client ALWAYs, literally 100% every time I play, crashes on those two levels. Sometimes my client crashes more than 2 times during ONE LEVEL. This is annoying since everytime I crash, I usually get killed since, well, I'm no longer controlling my avatar. ;)
The client also crashes even when I'm not in combat.
In addition, the lag gets worse when I'm in a group (more entities to render maybe?).

Now before you people go off on a tangent and tell me to get a new computer, I would like to say that THIS IS THE ONLY MISSION IN THE WHOLE GAME THAT THE CLIENT CRASHES ON!

For some unknown reason, the mission "Built to Destroy" always just takes an abnormal amount of my memory when compared to the other "boss" missions such as the Royal Jelly mission.
I feel there are some issues with the level that should be addressed and fixed, or at least the amount of icons and entities should be decreased.
It could be because the mission is one of the larger missions, I don't know, but pretty much it's the only mission that I have problems on.

I'm sure I'm not the only person experiencing an abnormal amount of lag on this mission, so hopefully the Devs will find the time to fix this level. I pretty much don't experience lag at all on this game except for this specific mission.

TL;DR The mission "Built to Destroy" has some issues that causes my client to constantly crash.