That is wicked looking!

Not sure how that's "Mature content", but lawl.

is that natural?

yep, strangely so! speculation is that its to attract bugs and spread its spores around.

It was really bright, enough to read headline font in pitch black.

Holy crap!

I had no idea ask did that. Unfortunatly, We have lost most of our ash around here due to that insect infestation, so I cant check this out myself :( Its also probably only at a specific time of year.

Well it was in late spring/early summer, you can find glowing fungus everyplace, you need to be in total darkness, away from any lights, let your eyes adjust and then look mostly ahead as you walk, you might see the flecks glowing out of the corner of your eye, the BW vision where its more light sensitive, if you get very close to it, a few inches, its easier to see. This stump was quite the oddity. A co worker saved a piece under his porch and kept it damp, it glowed for several weeks.