good work, like it, pretty solid <3 nice item choice

Get Shurelya's Battlesong instead of Eleisa's Miracle... It will help out so much better for you and your team and just so you know, Tenacity doesn't stack and you all ready have 35 from your Mercury's Treads.

Shurelya's Battlesong will make you more tanky anyways and it gives you CDR so you can use your CC skills more.

I've gotta say I'm pretty skeptical of the Eleisa's Miracle. Since Tenacity doesn't stack that component is made useless when you get merc treads. It's certainly not bad but I feel like something better could go there.
Other than that I liked what you had to share. +1 for sure

Alright, I suppose that makes sense... +1

I feel with the build he is tanky enough to do what I need him to do and I use the 9/0/21 for that extra damage/m. pen to make him viable as both a tank and someone who can dish out some decent damage. you of course could switch it to a defensive mastery set if you wanted but this is just my preference.

I am curious as to why you chose a 9/0/21 instead of a 0/21/9 or something. Let me know :D

Please give your ELO as well...Pretty good guide but I just want to know what players you are playing against. You should probably max out your W first, and your E second honestly...and Amumumu is a really good ganker and jungler, so early you might want to jungle instead of laning, or you could probably roam.