This Is the build I use EVERY game I use morde, regardless of the team-comp.

PROS
Passive shield
Able to make clones
Annoying to lane against

CONS
No CC

I go Insight Marks because It gives him a bit of damage output.
Vitality seals To give him a little more hp.
Magic resist glyphs because this build lacks some actual magic survivability thus making me a bit harder to kill.
Flat hp quints cause its cool yo.

I max E first Cause Its the easiest one to hit enemys with, Getting Q whenever I cant get E And I save W for last Because I find it the most useless.

Flash For Escape because ghost doesn't actually get anything done.
Ignite for the extra damage to get a clone.

I get asked this question A LOT.
And by a lot I mean almost every game, The answer is Because you have enough of a damage output as morde anyway, and if you stack hp with a thornmail its gg for any well put together team.
Then If it's a non put together team it should be easy anyway.

I play morde As a Mid and or solo.
I can and have done some 2 people laneing with him but I find that it doesn't work as well Since I consider morde the 2nd best minions farmer in the game.

Try to get in the middle of everything, The more damage you do the more they feel as you need to be focused.
So try to ult the main damage dealing ad champ as ap champs dont do anything for morde.

I love you guys <3