Disjunction

This achievement can only be achieved while doing a level with Spider, because she is the only character that can become invisible. Also it is very helpful to have the Shadow Strike Upgrade for this, as most enemies need more than one hit to be knocked out and this upgrade causes Spider to stay invisible after attacking.

Now knock down a stationary enemy who is in the path of a moving enemy. As soon as the moving enemy sees the body, he will start to investigate (question mark above his head). Become invisible () and knock him out. The first and easiest opportunity to do this is at the beginning of the level 'The Tombs'.