Halo Wars 2

This achievement requires you to get ten kills wishing four seconds of each other (similar to a Killionaire medal in past Halo games). It's recommended to work on this achievement during a Blitz Firefight match while going for the "It just keeps going" achievement.

If you manage to build a sturdy artillery squadron on the ridge in between Zones B and C (Blisterbacks usually work better than Kodiaks), then you should have no trouble killing the required amount of enemies within four seconds of each other by Wave 10 or 15.

If you're having some trouble getting this achievement by Wave 15, try to hang in there for a few more rounds; the longer you hold out, the more of a chance you'll have to call in additional artillery and reach a wave where it's mostly just Infantry Units, which are much easier to obliterate with artillery as opposed to Air Units or ground-based vehicles.