Going from memory, I believe this is Stage 2.
At the start of the level, there’s a giant skull in the middle of the screen, and loads of electric fences. You will need to get 30 deaths by electrocution in a single play of this level.
I found the easiest way to do this was to hide behind the fences in the bottom left and watch as the dumb enemies just charge towards you with no regard for their own safety. You will get quite a few down here before the screen automatically scrolls upward. After a wave at the top, the screen moves again, and there will be a few more fences this way. Just keep luring them towards the fences by hiding behind them and you’re golden.