Originally Posted by
Garlyle
Part of it has to do with just straight up skipping mobs. The keys do force certain mobs to be fought, but otherwise there's a few spots where you reach the boss and you can 'lock out' mobs, simply by having your tank stand just across the line while the boss fight is started by your allies. Once "[area name] is now sealed" pops up, the mobs are sealed off, the boss is fought as normal, and then you move on. They're not even fought.
That's what speedrunning is. Kill as little as possible, and when you have to, group up as many as you can possibly survive and then AoE splatter them, then move onto the next group.