On the post-game screen, show a tally of how many of each enemy had spawned and/or that you killed (and whether common/elite/champ), and also how many times each kind of hazard appeared.
Because, when you have one of those runs where you're like "there have been 18 singularities!" or "it just kept throwing eclipses at me!", having proof would be fun.
Under consideration Quality of Life User Interface