I've been an on-and off league player for 13 years now.
I've previously hit low Chall, and average around GM most seasons, I've started to play less as I have committments in real life that need attending, job, family etc. But when I do play, I tend to go up 200-400lp in a single day.
I've also been playing and coaching competitively for 3-4 years now. https://lolpros.gg/player/influentik, https://lol.fandom.com/wiki/Influentik

There's many VODS of me online aswell should you wish to look further.

I currently am more or less retired, and play competitive for the thrill of it with a group of friends, and soloq just on days I'm not doing much.

I'm a big fan of pushing slightly off-meta picks to win draft in competitive, and Mordekaiser is a perfect example of this, a lot of people, especially in higher elos/comp, are not used to playing against Morde, and he's been hidden buffed for several patches now, and has a legitimate place in the competitive environment due to his ult being able to take away a piece of the enemies' puzzle.

Will this guide let you reach GM/Chall with only Morde mid? No, he's not that strong and has clear defined weaknesses, but if you like the champ and have a bit of games on him, he can easily be fitted into the midlane role against a lot of matchups.

The midlane quests' boots are very VERY useful on Morde, you can get extra shield bash procs, extra omnivamp healing, more movespeed, everything really.
The 8% AD and AP increase also benefit Morde heavily, and is the main reason for taking him mid. When you ult someone, you steal their stats and that's added to yours. But this stat steal is also amplified by your midlane quest.

So let's say someone has 60 AD, you steal 10% of that, 6. and add that ontop of your (Assuming you have no AD items yet) 90 AD. you now have 96 AD. The midlane quest then ampplifies this by 8%, which puts it to 104 AD rounded up.
That's nearly an entire longsword worth of AD value, which then also equates to his Morde's obscene 180% AD ratio on his Q(Isolation)which means big damage.
This doesn't even take into account the AP you're stealing from AP champs too.
It's just super valuable, you become even more of a stat stick, and mid is the only role you can reach raid-boss levels of stat-stickiness.

I'll go over the main ones as I believe some are self explanatory

Dusk and Dawn - Morde has a 40% AP ratio on hit, dusk and dawn makes that 90% on each proc, earlygame, this is ALOT of flat damage. That doesn't even take into account his bonus health healing on proc and the extra attack speed it provides.
Riftmaker - A staple on morde, omnivamp is useful, and it increases your passive dmg and gets you more AP based on your health, which you like to stack. The CDR from dusk and rift combined also makes your ult have a very low CD.
Terminus - The new changes to terminus has made it so it has AD and AP scaling on it's on hit.
Dusk and Dawn already lets you proc it fast and get value from it, you stealing Ap and AD with your ult also increases Terminus's damage.
AND THE RESISTANCES IS WHAT HE NEEDS
Obviously it's not the best inslot every game, you can only really run it with dusk and dawn, but it's so insanely strong right now I'm expecting it to get nerfed.
Protobelt - The changes are actually better for Morde, as it increases his shield bash damage and makes him able to not get bursted in a second early game. The active is an auto reset too, which lets you proc your passive fast even as a rush item.
Rylais - Completely bait on morde, it's good in certain scenarios, but please stop rushing this item. You need to be a stat stick before you care about having enemies stay close to you permanently, and it gives NO CDR, you can't snowball on a 0 CDR item, but, in approach velocity builds, really insane.
Liandries - Don't build, morde has his built in liandries on his passive, and riftmaker is just better.
Bloodletter - Situation, but usually not great, try survive off of your E giving magic pen, and build more duelist-related items.
Deaths Dance - Insane item on Morde, lets you get your W off even if you're tanking a tonne, you have a permanent exhaust on the enemy, AND, if you ult someone and get an assist on someone else outside your ult (Quite frequently), the deaths dance damage gets cleansed against whoever you're 1v1ing in your ult, that means you're insanely tough to take down.
Wits End - Tenacity, 50% Attack speed, and a 50 damage magic damage on hit.
This is everything Morde wants later on in the game, and very underated as an item on him (His E pen increases wits end damage too)
Gunblade - The AD ratio on morde Q makes this item viable, but not a great rush item often. The active is useful as it lets you line up your E easier, and slow down the target you're ulting too, and of course Morde can appreciate the omnivamp.

That's it for now, most of the items Morde can build are VERY situational though, he can build anything realistically, as long as he remains a stat stick who can 1v1 whoever he's ulting, that's the power of this champ.
Obviously AP is favoured for damaage, but on-hit is not weak at all on him either, just mix and match for what's good in your game.

This is my first guide, so any feedback would be great, anything you found useful please let me know too as I plan on expanding my guides to champs more than just morde, as I play many other off-meta picks to a high level.
Big thanks to the lovely people on Mordekaiser mains who inspired me to create this guide - https://www.reddit.com/r/MordekaiserMains/comments/1v4dxyq/do_not_panic_morde_mains/

Thannks for reading, and I hope i've helped you out by making this.

- Influentik