Mordekaiser
Misery Loves Company
Lane harassment and consistent damage output.
Precision
Improved attacks and sustained damage
ConquerorGain stacks of adaptive force when attacking enemy champions. After reaching 12 stacks, heal for a portion of damage you deal to champions.
TriumphTakedowns restore 5% of your missing health and grant an additional 20 gold.
Legend: HasteTakedowns on enemies grant permanent Basic Ability Haste.
Coup de GraceDeal more damage to low health enemy champions.
Resolve
Durability and crowd control
Second WindAfter taking damage from an enemy champion heal back some missing health over time.
RevitalizeGain 5% Heal and Shield Power.
Heals and shields you cast or receive are 10% stronger on targets below 40% health.
Adaptive Force
+9
Adaptive Force Adaptive Force
+9
Adaptive Force 
Health Scaling
+10-180 Health (based on level)
Why Conqueror
Morde excels in extended fights where you're able to ramp your damage over time with your passive. Conqueror empowers that but dealing bonus true damage with every passive tick.
Why Triumph
Triumph synergizes well with Morde's [R] allowing you to come out the other side healthy enough to continue fighting.
Why Legend: Haste
Morde's biggest weakness is his lack of mobility and ability to be kited. You need to stick to your target to deal damage and Tenacity will go a long way in doing so.
Why Coup de Grace
Coup De Grace is the defacto damage amp choice, especially for Morde as you will be building a few health items.
WhySecond Wind
Second Wind is great for extended fights/trades allowing you to sustain health rapidly over time when combined with Doran's shield.
WhyRevitalize
Revitalize synergizes extremely well with Morde's [W], empowering both the shield and heal portions.