Probably unpopular opinion but Amumu has received a lot of indirect nerfs this preseason.

I am biased because I main Amumu but lately (4-6 weeks) I haven't played him much because he just doesn't feel so strong any more compared to other champs. The trade-off of pikcing Amumu is that you have a bad early and good scaling into mid-lategame but this isn't very true any more.

Earlygame

• Generally pretty bad. Very gated by mana. Also smite doesn't give mana any more.
• It has become harder for him to do the buffs on his own. The little guys gave him cdr on his E.
• He can't contest the sustain plant because earlygame he will get rekt by almost every champ. He is also bad at killing the crab.
• He doesn't benefit at all from the cunning tree. He is AoE so he doesn't take Savagery, with the loss of smite buffs Runic Affinity has become useless and if you want 5% extra damage below 40% HP you are better of using the Ferocity Tree where you can get 5% extra damage always.
• The Resolve Tree is pretty underwhelming for him as well. You only go deep to get CotC. You don't even want Veteran Scar because the 8% bonus shield is better and he doens't even have a shield in his kit. This mastery has become pointless. Also he doesn't have sustain and there isn't much to choice from pretty straightforward.
• Smite has become a pretty underwhelming Summoner Spell. For what it provides its cooldown is way too high.

• He has a comparative advantage for farming wraiths and golems. But the downside is he will have less lane presence.

Midgame

• Still very gated by mana. It is hard for him to farm and gank at the same time.
• He can only make 1 successful gank at lv 6 and has to wait 150s for his next successful gank.
• He lost a lot of HP. Strength of ages + Nerfs to Rylai = 400 HP --> x 1,15 from Cinderhulk = 460 HP less. Also Rylai is one of his core items and the buildpath straight out sucks now. He can't buy Giant Belt any more to provide the much needed early HP to cover for everything he has lost.
• He lost damage. Scepter changed, Rylai nerfed, Blue doesn't give AP any more and Gromp buff is gone.
• Abyssal Scepter doesn't benefit him much any more. 10% extra magic damage =/= 25 Mpen. Amumu only buys Rylai and Liandry for AP and relies on his base damage not his scaling. Therefore the 10% bonus damage is much worse on him than Mpen. +/- Don't need to explain Courage of the Colossus can be strong on him but it is situational. Its only strong when his ult is up and when he is close to a lot of enemies. You have these odd situations where you engaged on a champ with your Q but don't want to ult already but because you used your Q you triggered CotC and then within 30s you proceed to teamfight and ult and it is on cooldown and you just lost a big shield. Therefore I don't like this mastery very much.
• He still struggles to build mana/cdr. I think the best items for him are but you don't want them every game.

Lategame

• Is AP bruiser build has been nerfed really hard and has become unviable. I think every AP jungler is struggling nowadays.
• Lategame Tanks are weak by definition because they get 3 shotted by adc's.
• You end up being a walking ultimate that doesn't bring anything else to the team.

So Amumu got hit pretty hard with the recent changes these are facts. I recall Riot even mentioned he was a candidate for buffs prior to Worlds because he sees no play in competitive but he was ruled out because he was too strong in SoloQ, and especially lower eelos to receive buffs. Well at this moment he has definitely become weaker so it would be nice if he could gain some benefits from either

Some ideas

• Changes/ Buffs to Resolve/Cunning Tree that benefit him and in general AP jungler more.
• Revert his last nerfs to his E
• Give him a bigger manapool
• Introduce a new item for AP bruisers that gives mana/HP/cdr
• Buff Cinderhulk to +25% HP
• Make Giant Belt a recipe for Rylai again.
• Revert changes
• Smite gives mana and lower cdr