There might be more efficient way but this area is pretty neat to grind for the remaining upgrades.

The reason why this area is good because it spawns 12 spiky thingy every time you enter, so you can get 50-80 like every 10 second depending on how many times you've upgraded the drop rate.

For sure this achievement is already a lot easier on easy difficulty, but there's a guaranteed way to get this achievement in a single run.

If you feel like you're dying for some reason, press RETURN TO SAVE POINT, you can respawn on save point without adding to the death counter.