I'm a geezer (U.S. definition, not U.K.) by FNAF fandom standards. I was here for stuff like:
"Phone Guy was stuffed in Chica."
"Freddy can teleport into your office even if you have both doors shut."
"Freddy watches you on the first two nights so he can adapt to your strategy."
The Bonnie, Toy Bonnie, and Mangle gender wars
The height of Five Nights at F---boy's (still pretty solid from a gameplay standpoint if you're into RPGs; the Complete Collection rebalanced a few things, too, like Toy Bonnie's moveset)
That Purple Guy animatronic hoax
pole-bear's humanized animatronic designs being everywhere (still miss them :'))
Muse of Discord's old FNAF songs
The first look at Springtrap; we called him "The Salvage", and some even thought he was a form of Golden Freddy
The initial release of stuff like "Die in a Fire" and "5 AM at Freddy's: The Sequel"
Heck, the release or peak of all sorts of animations. "Fazbear and Friends," "Cheesy Death," "Freddy Head," "Foxy Gets Hooked," Crazy Boris' "Freddy's Troll Palace" series... A lot.
That one FNAF 4 teaser whose source code accidentally gave coordinates to a real-life pizzeria. The pizzeria was pretty cool about the situation and even did a little promotion for FNAF.
Three whole games released in the span of nine months (I wasn't here for the release of the original FNAF.)
Dream Theory and all the initial outrage around it
OG FNAF World--the one with the 8-bit-style world map
I know I'm in the prime of my life, but man, I feel old. TvT