Not big into the ultra stuff, think it's best left to Italians and French. I prefer the old school ways..
That said, I do love epic trolls, like that time where PSG fans did the "Bienvenue chez les Ch'tis" thing taking the piss out of Lens.
The back-and-forth between Verona and Napoli, where Verona had a banner with "Forza Vesuvio!" that the Napoli fans answered with "Giulietta è ’na zoccola" ("Juliet is a 'woman of ill repute'") is a classic.
Another good one was when the Lyon fans played on the class difference between them and St. Etienne with a banner that said "We invented cinema while your fathers were dying in the mines".
There's going to be a full stadium tifo at the Celtic Barca game tomorrow night. I'm excited to see what it's going to be like (although since I'll be there I'll have to wait until the highlights to actually see it).
If you drive down the Autobahn from Berlin to Leipzig, there's a few overpasses with some charming messages from Magdeburg fans on them, directed presumably mostly at Chemie Halle fans.
IIrC one reads (in German) something like "Only the FCM rules here, you c**ts" in massive letters. It's been there a couple of years, I imagine once it gets removed they just go back to spray it on again.