For example, in DAT file of boss spawn I have seen
[TREASURE]
<STRING>SPAWNCLASS:TREASURE_MONSTERLOOT_BOSS_ENGINEER
<INTEGER>MIN:1
<INTEGER>MAX:1
[/TREASURE]
[TREASURE_SECONDARY]
<STRING>SPAWNCLASS:TREASURE_NETHERLORD
<INTEGER>MIN:2
<INTEGER>MAX:2
[/TREASURE_SECONDARY]
[TREASURE_TERTIARY]
<STRING>SPAWNCLASS:TREASURE_A_UNIQUE
<INTEGER>MIN:1
<INTEGER>MAX:1
[/TREASURE_TERTIARY]
Can I add quaternary, quinary?
hi @zaynmalivn! i seem to recall a similar question maybe like 3 months ago, i'll try to find it.
im really not sure if we can go beyond tertiary (maybe search the other .dats?) or maybe one thing you can try is to edit the spawnclasses in those secondary and tertiary lines. you can make custom spawnclasses witha lot more loot and use those instead
hi @zaynmalivn! i seem to recall a similar question maybe like 3 months ago, i'll try to find it.
im really not sure if we can go beyond tertiary (maybe search the other .dats?) or maybe one thing you can try is to edit the spawnclasses in those secondary and tertiary lines. you can make custom spawnclasses witha lot more loot and use those instead 
Ty Phanjam.
After researching in GUTS I think I can confirm that we just have only three types of treasure after defeating monster.
According to mt mod merging I have to merge treasure itself.
Hey Zayn,
Making a custom Spawnclass is the best way to change what a particular monster or boss drops. You'll need to select the spawnclass in one of your boss' treasure slots, but the spawnclass itself can hold any number of items (at least, I haven't found the upper limit yet).