This was discovered by me and a few others in the Geometry Dash community, starting May 27th of 2022, and was developed further by me into this repo.
For this to work, you need a frame counter on item ID 10. The setup is shown below:
The inner collision block has a block ID of 1 and a group ID of 1. The outer one has a block ID of 0. The left toggle trigger disables group 1. Both collision triggers have BlockA ID 0 and BlockB ID 1. The first triggers on exit and activates group 2, while the second doesn't trigger on exit and activates group 3.
On the right, there is a toggle trigger activating group 1, with a group ID of 2, and another deactivating group 1 with a group ID of 3. Both are spawn triggered and multi-trigger. The pickup trigger increments item ID 10 by 1 and has group IDs 2 and 3, and is spawn triggered and multi-trigger.
Then, simply run the build script (b.sh) and it will add the RCE into your latest level. Do not open the level in the editor, as it'll crash your game due to the invalid data. Running clean.py will clean the latest level, removing the RCE from it and making it safe to open in the editor (note that this clears the guidelines).
This uses a specific version of gd.py (which is also patched), as others don't work with the weird encoding manipulation we do with the strings.