Doom first-person mode

[gorgias32]

I was watching Jack Danger's stream of the PinballFX cabinet, and while he was playing Doom the game switched into a mode I have never seen before - it looked like a "first person" view sweeping back and forth over the playfield with what looked like guns or arms on either side of the player. I just went through Shoryuken's guide and didn't see anything about this - what happened? How do you activate it?

[DepecheM101]

It comes up as one the random rune trials which can be started by shooting the left ramp with the three runes on enough times.