Welcome to the Unkillable Carry Yuumi Support Guide:

This guide is about making a single person as hard to kill as possible whilst making them impossible to ignore.

Healing can only ever do so much; the limits to healing in league are as follows….

The carries max health (You can only heal as much as their health allows)
How many items you have (You can only heal as much as your scaling allows)
How quickly you can heal (If they are an assassin they could do all the damage before you could react to it making it worthless)
Your total amount of mana (You rush through mana incredibly quickly as Yuumi and if you have none then no more spells for you, meaning you are fairly useless whenever you need more mana and your passive is not up)

But what if we could fix some of these problems whilst making use of more of Yuumi’s innate resources at the same time?

Cue Knight's Vow, this one item alone gives Yuumi 13.1 Health regeneration at level 18. But the thing we are interested in is it’s 15% damage reduction. Being the untargetable cat that yuumi is, she has little danger of dying due to being at 30% hp and can always be next to the carry to provide them with this damage reduction, not even needing to be on the carry for it to work. Previous iterations of this build needed warmogs to regenerate the health yuumi lost. But it turns out yuumi has 1700 hp with both moonstone renewer and knights vow making it so the carry needs to take 7000 damage at once for the 15% damage reduction to stop taking effect. But since the one item alone gives yuumi 13.1 hp regen per second it allows her to stay out in the field on her carry for a long time without running out of hp. Meaning the item can be a standalone purchase giving the build high flexibility which is needed nowadays for solo queue and a 3000 gold lower cost than before.

This one standalone item fixes the following of yuumi’s problems…

How many items you have (The damage reduction reduces the amount of healing your items need to provide by 15% meaning you can build more of other items without sacrificing your healing)
How quickly you can heal (The extra damage reduction reduces the opponents burst rate by 15% giving you a greater time to react to it and save your carry)
Your total amount of mana (No longer shall yuumi have to be useless when she needs more mana, instead being able to provide damage reduction whilst she is waiting on more mana)

So by building this item you are essentially giving one person nearby support without needing to be on them, allowing you to provide support to two people at the same time in totally different ways. And since this is a standalone item, the rest of the build is highly flexible, meaning different mythics are an option. But in my opinion the best mythic for this build is Moonstone Renewer. Due to the mythic giving healing that synergises well with the 15% damage reduction and is a nice first item pick up. You also shouldn't take potions or wards early as it allows you to get a item slightly earlier than normal.

Also as a fun side note, my first ever game using this build was when my whole team was feeding except for me and a master yi. I just stayed on him the entire game and we were having fun getting targeted the entire time. We got 2 quadras that game by ourselves and nearly a penta if I hadn’t stolen it off master yi :).

Summon Aery gives a large amount of bonus shielding and healing for minimal effort making it the perfect choice for the build.

Manaflow band gives the extra mana regen yuumi needs to have plenty of mana during the laning phase.

Transcendence gives ability haste making yuumi able to heal the carry more often.

Gathering storm gives yuumi a large amount of damage and more healing late game.

Ghost poro is the best rune for yuumi in the domination tree as apart from the final row they don't do well on yuumi for various reasons. Going this over zombie ward as you won't always be able to stop to clear a ward to get the free ward or be able to stack it so easy early.

Ingenious Hunter is a major rune in this tree due to its item cooldown reduction allowing yuumi to use all the passives she has way quicker than normal.

You might be wondering why you see the following items in the builds section.
Banshees veil, frozen heart, randulins omen and vigilant wardstone.

But they are here for various reasons which I will go over now.

Banshees Veil v Mikael's Blessing
Ok so here you can either build one or the other or both depending on your needs.
Against someone like Leona or Ashe you would build banshees veil because as yuumi you can jump off your carry to block the ability from hitting your carry thus voiding the stun and damage. And it gives plenty of AP and AH making it perfect for yuumi to pick up against them and it has a less than 40 second cooldown allowing you to block 3 stuns or abilities compared to Mikael's 1 cc ability every 2 minutes or less.

But against someone like Anivia whos stun isn't targeted you are better off getting Mikael's Blessing as Banshees veil will not work against them.

Frozen Heart can reduce any fed Ad carries attack speed, so build it if the enemy if fed with a lot of attack speed and damage. How ever randulin's omen would be better against Jhin due to his attacks scaling with crit and frozen heart will not effect him.

Vigilant Wardstone gives a tonne of vision making it perfect for protecting from enemy ambushes. Keeping your carry and your team safer. The 12% extra hp, ap, and ah is always nice and the extra control wards are great against stealth champs.

For this build split pushing carries or carries that can take and dish out a lot of damage are best.

As a split pusher you should be taking demolish to threaten turrets and their base, to get them to have to respond to you as yuumi can tank the turret for you and the enhanced minions will continuously be lost to the turret if no one responds, giving gold and exp to the split pusher plus tower gold. And due to yuumi being there and the split pusher having high resistances they will likely need to send multiple people where you can get away using knights vow on the carry if you decide to build it on the carry as well.

Hullbreaker still works when yuumi is attached to you so you basically have the bonus resistances + the damage reduction, healing, better minions.... You get the point.

Building Knights vow on the carry here has a funny yuumi interaction, when yuumi is at less than 50% hp you get 35% perma movespeed as turns out when she is on you you are always running towards her. (This might have changed but as far as I am aware it hasn't) Meaning a champion with 400 move speed would get 140 bonus movement speed. Which is crazy. Meaning yuumi can tank turret to bring her hp down if someone is coming and the enemy team will be saying, bye bye split pusher!

With deaths dance on the carry it delays their death, allowing yuumi the chance to heal them up during the fight and giving a higher chance of getting takedowns.
A very good item for the build.

Immortal Shieldbow gives a shield which allows the yuumi to prevent even more damage as 15% of the damage of to the shield will go to yuumi instead acting as if the carry has more hp instead of a shield and it allows yuumi to get more heals in.