You could always have enemies carrying keys and things like that to hinder casual speedruns. Another option (although a bit more advanced) is to give enemies abilities like grappling hooks that pull them around or you towards them.
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Indeed. As a matter of fact, I'm currently working on a full version of the game, spanning a planned 10 level duration.
I currently don't have any plans to have enemies dispose of essential items when killed, but I do intend to introduce a key and door mechanic, along with a few platforming sections spanning various biohazards, which in and of themselves, will enforce a certain manner of backtracking and enforcing a more precipitous pace from the player.