Watch Dogs

You'll first need to unlock the Focus Skill. It can be found in the Combat section and can be brought for 1 Skill Point. If you have 5 spare Skill Points for the 'Improved Focus' and 'Slowed Focus' upgrades, then it maybe worth purchasing these, but it is possible without them, though it will be a lot harder if not near impossible. Once you've acquired this Skill, you can now slowdown time with your Focus by pressing in .

Once you've purchased the Focus Skill, you'll now notice a wavy white bar with 6 squares in the bottom left corner of your screen. This is your Focus meter, and when being used the square blocks will disappear until all are gone. Once all 6 have vanished, then your Focus has run out and you'll be placed back into normal speed.

This can be attempted on either gang members or the police, but doing it either in one of the many Gang Hideouts or ctOS Centers will be the easiest option. When you choose your location, simply scout the area and tag as many enemies as you can. You'll now need to bunch 4+ of them up and this can simply be done by a well placed luring gadget or by hacking something that'll explode. In most cases, more than enough enemies will gather to it's locations.

If there's now enough enemies within a short space of each other, pull out your gun and press to trigger your Focus. Aim for the head, as even with the 2 extra upgrades your Focus doesn't last that long. Once 4 enemies have been killed within your Focus timeframe, the achievement will unlock. If you don't manage it, simply play a bit of the game or run around the city doing this and let your Focus replenish until you can attempt it again.