So there's a funny story behind this one... Our maths guy tweaking the mechanics of enemy spawns has a deep passion for this sort of thing.
One night we had this exchange:
Maths guy: Woah this is intense!
<Some time passes play testing>
Maths guy: Guys! I've mastered Endless mode! I will never die!
Sound guy: But Maths guy, you built the algorithm XD
Needless to say, we learned a lot from building this and this is great feedback. Thank you!