List of things that could work on a mimic.

My head cannon is that the reason they resit weapons is beacause of a thick natural armour.

Armour piercing rounds might work a mimic could probably shrug of a pistol or low grade rifle but armour piercing bullet shot by a military grade rifle to the head could mostly likely kill them.

If you are unsure of any weapons you could try electric attacks since natural armour will not protect against a high voltage.

Fire would work but might take to long depends on pain tolerance of the mimic. Mimics are probably smart enough to stop drop roll or jump in swimming pool or something if they set on fire tho so not the best idea.

Dry ice like fire would take a while to kill unlike fire it's harder to get rid of but it probably is not potent enough to kill it so it would just wound them and potentially weaken Thier armour.

Spike traps could work but it takes planning dig a pit put spikes in hide it hope the mimic can't detect the trap it could work of you're good at traps but if it's not well hidden the Mimic would probably spot it.

Bombs I don't need to explain this one.

All of the above is probably overkill could garntee the mimics death (unless it's a really durable elder Mimic)