Well, Amumu is now atrocious

Even though he was used as the archetype for what tanks typically do/are, Amumu is in a much worse spot now than he was even before the 7.7 update. Jungling is much more painful, his kit now encourages you to build more ap or else be ignored after your ult is done but he has no natural tankiness, and to engage he either has to flash ult or use q which has terrible cooldowns and is fairly easy to avoid unless he walks right up to you.

His new passive doesn't feel like it helps the team. Is 10% really going to make a big difference against a tank? And that means amumu needs to stay on/near enough the tank rather than tying down squishies. Is it supposed to encourage your team to build more raw ap rather than penetrations? If it comes to dollar for dollar, penetrations will deal more damage than raw AP most of the time even when considering amumu's passive. Is it just a raw damage buff? In that case, keep it as that - a slightly higher % raw damage buff (which helps amumu in the jungle as well).

Amumu's w deals percentage of health per half second. Shouldn't this feel better against high hp targets (ie blue buff and red buff) then straight damage? But no, the decision was to nerf the % of health and buff the damage per second - W is now a crappier version of E. There used to be a debate between leveling w and e first (w = higher dps lower mana, less burst no resistances), now you get a single level of w and ride the game on that instead.

I'm an amumu main and I've really struggled in season 7. But 7.8/7.9 definitely feels the worst.