What I've tried so far in URF
Yasuo - uber fail on my part due to Q only being reduced through attack speed and E still limiting dash to the same target over 7 seconds. Worst game of all that I played
AP Rammus - Permanent taunt and ball knockup. No one is getting away from you unless they bring QSS
AP Cait - Fun, but permanently trapping people with her snare never worked out. Need moar CDR.
AP Jax - Worked pretty well. Stomped an AD Malz in lane using this but lost the game due to his tower pushing.
Azir - Thankfully he gets the CDR applied to his W as well. Dashing around is super fun
Bard - Land a Q against a wall and it's a permastun. Even went on a killing spree. Magical journeys EVERYWHERE. Got some pretty nice ults off for my team as well but I still got blamed for the loss. QQ
Karthus - Ulting every 40 seconds is pretty silly. Keep E on forever and wear out your Q key.
Hecarim - Broken but I'm awful at him. Should stay banned.
Sona - Should be permabanned. Nothing more to say
AP Tryn - Fun and silly but can be kited. Overrated
AP Panth - 1 Second stun on a 2 second CD. Strong but generally needs some followup, otherwise can be outplayed too easily.
Garen - Permanent silence. Can't run away from him, can't fight him. Stupidly awesome. My favorite match so far.
Cass - Not as strong as I thought it would be. Her ultimate animation is too long and too obvious, her E is already Urfed in normals and poison needs time to deal all its damage... time that other champs can use to just burst you. Wouldn't recommend unless you already play Cass.
Darius - Get ahead, stay ahead and kill everyone. Q on a 1 sec cooldown. Pull them in, hit a slow and they have no chance.
I'd encourage everyone to use this mode to just go ham and make the craziest flash + ultimate plays you can think of and to use this to practice champs you wouldn't normally dedicate the time to learn. Urf is a severely underrated learning tool.