It use to be, that the celebration of WrestleMania would end after the final bell rang.

That is not true.  The night (or nights since the brand split) after WrestleMania is rather eventful to say the least.

The first real great moment after WrestleMania came on the night after WrestleMania XI.  That was the night when Alundra Blayze and Bull Nakano squared off in a Women's Championship match.  A match so good, that many people believed that it should have been part of WrestleMania, which was judged by many as the worst of them all.  Who knows how much better the card would've been as a whole, if they had given these two women a chance.

Other big moments from shows after WrestleMania included...

The new DX forming (WrestleMania XIV)
Hulk Hogan ditching the NWO (WrestleMania X8)
Brock Lesnar's impactful debut (WrestleMania X8)
Goldberg arrives in WWE (WrestleMania XIX)
Ric Flair & Shawn Michaels' retirement speeches (WrestleMania XXIV & XXVI respectively)
Dolph Ziggler cashing in Money In the Bank, and winning the World's Championship (WrestleMania XXIX)

... and of course, the Fandangoing.

What are of your favorite moments from the RAWs and SmackDown after WrestleMania?

Hogan leaving the nWo holds a dear place in my heart because I was at X8 and was part of that crowd. We Canadians take full credit for Hogan turning face that night. No, it was not the plan all along like you may think. It was all us. We did it.

I liked seeing Goldberg make his debut. That was pretty wild.

Ziggler's cash-in was one of the best pops ever, total surprise.

I can't remember any other huge moments.

I don't know what to expect this upcoming Monday/Tuesday, but I have a feeling that we'll see Samoa Joe return to Raw on Monday, probably to crash Roman's Universal title celebration. It's also possible we see Jeff Hardy return as well, since he's booked at the Greatest Royal Rumble at the end of the month.

Bret forming the Hart Foundation with Owen & Bulldog the night after Wrestlemania 13 is #1 and the best.

Night after Wrestlemania 14 also deserves a mentioned- X-Pac returning, Double J's epic entrance on a horse, Austin vs. Vince stuff, and the New Age Outlaws vs. Hardcore Legends cage match main event where the new DX was formed.

While it didn't really heat up until the past few years, I feel like the Raw after Wrestlemania has been a low key "thing" since Sid turned on Michaels the night after 11.

'98 really set the tone for the rest of the year. They doubled down on the Vince/Austin act where they had Austin pose as the Corporate Champion, only to lay Vince out with the stunner and get arrested for his troubles. They announced an Inferno match between Kane/Taker which was just the perfect car-crash stipulation the Attitude Era was known for. Farooq was booted from the Nation and Rock became the leader and then of course you have the stuff with D-X. A huge show, why wouldn't you change the channel with all this happening?

One that hasn't been mentioned yet is 2012. For the most part it was just a ho-hum show, but the return of Brock Lesnar was one of the biggest pops of the modern era and one of the few rare must see moments. Also supposedly Lord Tensai debuted on the show as well, that has to count for something right?

Normally just the debuts/returns. Goldberg’s debut, Lesnar’s (?) debut and return. I also think Umaga made his debut from memory.
Sadly NXT kind of takes away from “new” debuts now, last surprise was AJ Styles.

The RAW after Mania is usally one of my favorite things about Mania weekend (crowd not withstanding). For me it's a more personal choice as I was at 4 RAW after Mania's in person (WM 24-27) so I've been in the crowd to witness Ric Flair, HBK and Edge retire. I also was 10 rows away from The Rock which if you know me knows that it is not close enough but I'll take it.