Cool video—how was such fluid 3D achieved on the GBA hardware? Anyone know of any war story articles about developing 3D games on the GBA?

Low resolution combine with a decently fast processor means software rendering is entirely doable. It's a comparable situation to very early PC 3D gaming.

Just for the record, "decently fast" in this case is a 16 Mhz ARM 7.

It's especially crazy that a bunch of them look to be rendering legit polygon scenes— this isn't early nineties 2.5D titles like Doom and Wolf3d running on 486 PCs.

The ARM 7 is a pretty good processor, so it can get a lot done on 16 MHz. Quite a bit more than what an x86 of similar clock speed ever could.

Ok you could argue that’s more complex on the GBA.

I would argue otherwise; interfaces to other people’s stuff always are the most difficult parts of programming. When you do it yourself (3D projection etc.) it’s just you and reason and that’s not so bad.