Are your players getting a little too confident? Do they feel like they can just run up to monsters and hack away at them without any tactics or preparation? Death Burst may be just the trait you’re looking for.
Death Burst triggers when the creature dies, typically dealing damage to other creatures within a specified radius of the “burster”. Some monsters with this trait cause blindness, such as the dust mephit. Others have a death burst, but it’s called something else, like the Colossus of Akros and its Crumbling Destruction trait, or Death Throes for draconians
|Colossus of Akros||23||MoT|
|Draconian Foot Soldier||1/2||FTD|
|Gauth||6||VGM or MPMM|
|Spirit Statue Mascot||1/4||SCC|
You should consider the environment for the encounter as well. Make sure to keep spaces enclosed so that the burst is harder to avoid. Shut down long lines of sight with objects. This will make it harder for your players to snipe the enemies from a safe distance. Also, consider sending an NPC in first to get a taste of the sweet burst so that your players know the stake. Unless you’d rather they find out the hard way.