I wached this video:
This is where the 120 ft decision height really comes into play. I'm not very good at English, but I think this refers to the stoppage of only one engine, not two. Land below 120 ft, continue the flight above it in one engine mode.
I think this because every helicopter has a height/velocity diagram, on which the areas where a safe landing is not guaranteed are marked. I couldn't find the EC135 anywhere on the internet, maybe because it has two engines. That's why I'm uploading a diagram with a single engine, the EC135 can be almost similar without an engine. This shows the approximate altitude from which you can land safely without an engine starting from a horizontal speed of 0 kt.
Here is the article:
Yes, you can try autorotation from 500ft.
You won't succeed landing this thing.