Sion's Passive
Sion has the most fucking useless passive in the game. His passive takes too long to activate, then when it does activate you can't even use it because they are too far away, have a stun, snare, or some form of CC, and the speed buff is entirely useless because any AoE or single target slow stops it completely. By the time the slow is gone Sion is already dead. His passive is shit. His passive needs to be reworked so that it can actually be used efficiently, instead of just instantly losing all health in the next 3 seconds, and never being able to hit anyone once. Plus, Sion's attack range and animation just makes it even harder to even use an attack. The moment Sion tries to attack, all they have to do is step back and his attack animation is cancelled.
Even in the middle of a team fight, his passive is entirely useless. Sion get's caught up in AoE CC, then can't even move quick enough to deal any damage. Even Karthus has a better passive than Sion does without any movement. Karthus can at least deal damage because he is invulnerable to everything. Sion should at least be invulnerable to CC.