Summary:
Dark Retribution 5* Operation Crimson Hammer reward bomb does not damage mini-jellies in Royal Jelly Palace.
Tried only with 5* bomb. Mini jellies walk through it without getting hit. And the damage it does is also minimal, so I see no use of this bomb (I also haven't seen anyone actively using this bomb either).
Dark Retribution does not damage mini-jellies in Royal Jelly Palace
Irthan
I disagree. There is no such thing as "monster size" in description, no other weapon has such limitation, thus its a simple overlook from developers.
It's because all the other bombs are ground based and this one is supposed to hover above the ground or something like that.
So they likely intentionally made it so that minis wouldn't be affected by it.
A much bigger problem is that they can't damage the battlepods in the Seerus fight, where it would otherwise have been incredibly useful.
Give the bomb a chance, though! It does incredible damage to pretty much everything but fiends. Even undead can be killed at a reasonable pace.
Flowchart
Its a damage bomb - it should do damage to enemies. If it doesn't damage some enemies without a proper prior warning, its a bug.
If you use the Dark Retribution against the mini-green slimes, they get hit by the bullets. The green slimes are of the same size as the purple ones, so a height issue doesn't really seem logical here.
Not a bug. Mini-jellies are too short to get hit by it.