A bit mechanical, lots of skill shots, but each have powerfun ap builds

might be perfect for you. He has some half-tank, Half-mage builds that scale really well, or you can go full one way or the other. Only has one skill shot. Highly recommended
Edit: since everyone else is suggesting it, here’s some Amumu builds to get you started (order of items somewhat situational)
Full Tank:

Tank/mage:

Full mage:

only tankier late in the game, but you run in at Mach 5 and oneshot some poor fool. Fairly simple besides learning his Ult combo. Great AD option.
you role into some, new activate your bonus armor, taunt, and they kill themselves. Really easy champ but not really any viable ap builds
probably the highest skill floor out of these (not very high though), but really easy once your there.
Edit 2:
if you want one champ that can do it all, here’s your guy. He is really able to fill any need your team has, with a variety of builds. Any build with
becomes a magic damage build. Anything with
becomes a physical damage one, and anything with
becomes really tanky. Here’s some examples of builds you can try. They mainly consist of the same items, just what order you build them in.
Tank rush build:

Magic damage:

Extra Physical damage:
