the screen with an 8-player session in act 3 is one that a lot of people know, but calliope's existence was hinted at as early as act 4. jake's letter mentions his arm being twisted by someone else (callie) in order to make the liv tyler bunny...

also the opening of act 4 flash has a lot of fun easter eggs, dropping the gushers will produce some you can use to heal, the barbasol bomb explodes. i used to like using the hammers when i was younger, but sylladex based combat is fully operational in that game. i liked tp have a row of sylladex cards filled with heavy items, and then would just pick something up to start the cycle of endlessly throwing shit out and picking it back up