This is pretty much what playing Eberron was like for me, but all of these were PCs.
Suddenly, airship pirates attacked! To be fair, one of the second level PCs had gotten to roll the random encounter D100, and had rolled a two. This meant that there were two ships of airship pirates, and they had flying skiffs and were relatively high level. We were proper fucked. Three characters went down in the first round (the low level ones, of course). Our sixth level Dwarven Cleric started working overtime, the fourth level Druid started in as a backup healer, and the Shifter Artificer (our main source of getting out of dodge) said she was going to summon a monster. Her player reached into his backpack, grabbed a stack of Monster Manuals, and started paging through them.
And then he pulled out a stack this big, I swear...
If you had to look something up, you had three minutes and then your turn was skipped. One of our most powerful characters hadn't finished leafing through Monster Manual 1 in three minutes, and initiative went on. My cohort Cleaved through a few guys. I Inspired Courage and picked a guy off with my rapier. Initiative rolled on. The next round (about 45 minutes later, because have you ever played with fifteen people in the same game?), our Artificer was on Monster Manual 3 and showing no sign of picking what monster she wanted to summon. Her turn got skipped again. The Druid and Cleric and most of the rest of the party went down, and I, as the only person who could cast healing spells who was not interminably summoning a monster, stepped in to start reviving people with my Bardic Cure Light Wounds.
Combat went really badly after that. We started getting kinda hostile over the next hour and a half and three turns that the Artificer poured over Monster Manuals, Fiend Folios, The Eberron book, Pamphlets, and PDFs to figure out exactly what he wanted to summon. I managed to waste my highest spell slot on a Mass Cure Light Wounds, the newly revived Druid summoned some wind to stop the second wave of pirates from landing that turn, and the low level characters and animal companions dragged the three characters who were still unconscious into the hold with the beat to shit Cleric for some band-aid time. The rest of us braced for the second wave of pain, low on hit points, low on meaningful spells, and low on hope.
The GM decided to have a smoke break. "Are you ever going to do anything?" I asked the Artificer's player. "Just gimme a minute. I need to choose between two templates," he replied, sitting calmly and jotting down stats of...whatever it was on a piece of notebook paper. I rolled my eyes, grabbed the character sheet of the friend who had never played before who had showed up for her first game ever, and started explaining to her how to fight defensively and how flanking worked. The GM came back, a few of us bought pop at the counter, we settled in, and then the Artificer spoke up.
"When it's my turn, I summon a Celestial Dire Bison."
The literal fuck?
The room grew silent. "Well, the pirates go before you," the DM said, and proceeded to describe them landing and mobbing our vanguard. Then the bison appeared in the middle of the deck, spread its wings, and then, you guessed it, bull rushed the entire end of the ship. Five pirates, two PCs, and a wolf animal companion went overboard. Everyone was dumbfounded, and we watched over the next two rounds as a flying bovine wrecked two shiploads of sky pirates while we used Levitate, Tenser's Floating Discs, and rings of Feather Fall to save the party members who went overboard.
But we got saved by a fucking cow. With wings.
And that, ladies and gentlemen, is the craziest roleplaying moment I've ever had just from pure shock value.