First the Claymore; if for some reason you Don't know what a claymore is I'll describe it:
Its a nasty square booby-trap that attaches to a wall or any flat surface.
Once attached it arms in 10 seconds, anything that is not human and moves close enough to it will cause the mine to detonate. With a good blast radius about 1.8 times that of a grenade, it will cause mayhem.
Its also 300 Credits, and you only get to hold or deploy ONE at a time.
A remote detonator is available. (once you stick it on the wall you keep the remote) Also the remote detonator can be used while you are still holding the mine. Kamikaze's optional.
The Invisi-Dretch:
A Tier 3 upgrade to the normal dretch that:
(this is a free-upgrade)
Makes it invisible when not moving fast. Yep, 99% invisible.
On walls, on the floor, anywhere its nearly invisible, so long as it does not move fast. Walking speed only for invisiblity, right?
This is a PASSIVE ability, it costs nothing, needs nothing, its always on (except when running).
Helmeted Humans, Tesla coils, and people with 20/20 vision can pick out Invis-dretches really easily in well lit corridors... but how many corridors are all that well lit?

Also it has the unique ability to Throw its 'Voice': You can use the skill to confuse and terrifiy any grunts that dont notice you nearby.
When you use the 'growl/yell' action any humans you are targeting will hear at random a dragoon/maurader/tyrant or other alien noise DIRECTLY BEHIND THEM.
Think of the fun that could be had. A Dretch will get shot to ribbons super fast at S3, and cant hurt anything really. So wheres the harm?