Itachi's transformation is the hardest in the game to deal with...you can't just throw at him to knock him off stride like other transformations. Deidara is the most annoying and spammed character...I refuse to fight him regardless of the circumstances. Any puppeteer user about jonin level and higher is tough to beat. Minato, Sage Naruto, and Killer Bee's transformations are tough but beatable.
The online play in generations should be better because they're supposed to be balancing the characters more hope that means no more spamming Deidara...I can deal with overused ninjutsu's, guys who have to transform to win (so they use Minato and Itachi), and even puppeteers (I give props to the skill) but I can't stand Deidara users. They should just stop playing, it's not even fun...literally pressing the same button until your opponent is dead...ugh