INVERSUS Deluxe

This achievement can be a little tricky, I recommend playing on the default arcade map as it has an open area and large groups of enemies spawn on the edges consistently. It’s important to use charge shots on more spread out enemies and single shots on large groups. Try to move around to bait them into moving together for extra combo points, while not necessary for the multiplier it will spawn you extra ammunition and clear out more of the area. If you die the multiplier resets, so instead of using your lives I would say just to restart the level. Maximum multiplier is 9 and the achievement popped when my score was around 500k but it will be different for you depending on your chain hits.