Complete Ymir Guide (v7.5)

Ew

This is a terrible support build

Since you ask for criticism here we go:

So let's start of with your listed relic choice. Like other said meditation gets outclassed by Magic Shell. Early game it is a little better as the mana sustain it provides can give you an edge. This mana sustain falls of the longer the game goes as items provide the needed regen.
The healing is outclassed by the shield from Magic Shell. Especially late game when Magic Shell provides 2 block stacks while meditation gets hit by anti heal. The cdr and reduced mana cost from med is not gonna help someone that is almost dead in most cases.

Now to the build itself.

Your start is possible although not my preferred choice unless it's a hunter warrior support lane. I myself prefer Boots to help me stick a bit better to their adc (who usually does not start Boots) or get out of the thick of an aggressive play. Still this is more a playstyle thing and not necessarily a bad start. Also I would recommend swapping the Mana Potion for a Multi Potion. They stack with health potions (and since you run med mana should not be a big problem anyway).

Easily said starts for support can be really different I have even seen upgraded Magic Shell starts. This one can be seen as a regular start.

So moving on you rush Sovereignty. Not a bad choice (unless your opponent is a mage adc, however in that case I assume you go for Heartward Amulet). One problem vs the regular boots rush most supports do is that if the game calls to be rotate heavy you will get out rotated early. Of course if it isn't it will give you an advantage. Be aware that staying in lane while the other support is rotating can hurt your team more than theirs as long as you are not successful pressuring out the enemy adc (which is hard if they stay back enough unless you have Blink Rune.

Moving on shoes choice is good. Pestilence also a good pickup to counter their healing. Do be aware there are more options for magic defense that can benefit your team just as different boots can benefit you.

And then we see a shift towards health. Well just grabbing health is pretty bad and those ~120 protections (which will mitigate 55% of damage) you have, will do something but not that much the moment mages or adc get their percentage pen (reducing your 120 prot to ~76 (3 The Executioner stacks reducing your mitgation to 45%. A 10% damage increase. Combine this with some staple items being Soul Reaver and Heartseeker (or Qin's Sais) and you will get melted.

On top of that both Mail of Renewal and Stone of Gaia's passives are countered by anti heal. My recommendation would be to grab the staple support item Gauntlet of Thebes instead of Mail of Renewal. This will provide you with another 60 prot when stacked (giving you 65% mitigations without pen 55% with pen) and your teammates 10. You will give up the small bit of CDR but keep the health. Another option would be to grab Spirit Robe or Mantle of Discord however then you trade the health for the cdr.

Last big points are the amount of cdr (20% is not much and after swapping boots 10%) is a bit low to control a teamfight later in the game. While 20 is decent (I prefer 30) the 10 after selling boots is just to low.
And no counter building options like spectral armour, midguardian mail etc. these can be really helpful (stone of gaia is a counterbuilding item agaisnt heavy knockup teams).

Then moving to your boot substitutes I would not bother with any of them. Honestly I would have been happier seeing Chronos' Pendant, which is a bad support item too.

While I don't mind a bruiser support style this one kinda lacks the proper protections for it. In higher lvl of play it will hurt your team more often then not as your frontline will die faster in teamfights. In this build case the moment you go and ult you can end up being burned down as you're rooted in place. That Hp5 is not gonna matter when you get hit by ~2-2.5 400-600 damage adc auto attacks per second.

For a bruiser build I would add at least 1 high prot double prot or 2 one type of protection items (may contain power like Void Stone).
For a support build I would add at least 1 double prot and 1-2 one type of protection items or counter building item. Moving Ethereal Staff as boots replacement.

I would add Spirit Robe, Mantle of Discord, and Polynomicon as your situational items instead of what you list because the passives of spirit and mantle are good for heavy CC comps, and poly's passive is great against objectives. Pythagorem's Piece isn't a bad item either, but you generally don't need pen items like Divine Ruin on a support (outside of Void Stone), especially if someone else has already built it because the item's aura doesn't stack.

Stone of Gaia and mail of renewal aren't good items. Magic shell outclasses meditation