Just did 4 more runs
#1 - Kill random mobs and the 2 bombs, but not the mites = got 1st chest
#2 - Kill random mobs and the 3 mites, but not the bombs = got 1st chest
#3 - Kill random mobs and both the 2 bombs and the 3 mites = got the 1st chest (so mobs are not exclusionary)
#4 - Kill random mobs and neither the 2 bombs or the 3 mites, but killed 3 flans on the path back to the terminal (in that round bit with the vertical spoke near the middle of the map) = got 1st chest.
I want to do some more control testing with those 3 flans, but it seems that there are 3 mobs / groups of mobs that act as triggers:
Now consider the following chart. There are 8 kinds of mobs in the dungeon and 4 zones, for the start and the 3 areas unlocked by the terminals. Pterocs and Mitetraps are found in all 4 areas. Lice and Lanterns are found in 3 areas. However, Saplings, Flames, Puddings and Cell Mites are only located in one area each. I wonder if there is a 4th kill mob (a sapling) in the first area?
Also I wonder what would happen on a run where you killed no mobs except for the target bomb, puddings and mites?
Oh and fun fact, I counted and i think there are;
34 mobs in area 1,
32 in area 2,
42 in area 3,
49 in area 4,
for a total of 157 mobs in the dungeon (excluding bosses and adds)