It needs to have a few tweaks tbh, realistically there's nothing to stop you going a full team of Karthus's.
IIRC Karthus and Teemo are autobanned. Even for a 'fun' mode they were considered to toxic en masse.
Played a couple of games, it's alright but can be one sided if people are too rigid in their play. Had a great game as 5 Evelyns vs 5 Ezreals where they were strong early but ended up losing to the endless onslaught of stealth picks once we got the idea of a laning phase out of our heads.