The promised level editor for Hotline Miami 2 [official site] is "pretty close to completion", developers Dennaton Games have explained in a a recent blog post. The editor looks to be pretty full-featured, allowing you to create anything from a single level to a full campaign with cutscenes.
The blog post gives a step-by-step walkthrough of the editor's UI, as well as the various options available. There are some caveats, however. Some limitations that, while they aren't game breaking, could be disappointing to some. The main one being that only certain enemies will be available for each of the protagonists. Which means you won’t be able to create a level containing every enemy type in the game. A shame, but not a deal breaker.
The cutscene editor is also fairly rigid. You should be able to do whatever you desire within it, but careful planning is required because of the way the editor is structured. Notice an error early on in your cutscene and you'll need to delete everything you’ve created since then to go back and fix it. Something to keep in mind.
Despite the editor being in the final stages of development, the developers seem open to feedback in case you feel they've missed anything important. It all seems pretty simple and drag-and-drop and judging from the screenshots Dennaton has already proven how easy it is to make penis shaped levels. So expect lots of those.