Pretty bad to be completely honest.

Items, Runes, Masteries, all over the place.

If you're going to build that Randuin's, I would take advantage of that Heart of Gold, and buy it before working on that Force of Nature. The effectiveness of FoN's unique passive is relative to your hp score, so getting the full item so early is a net loss in early game effectiveness.

Building piecemeal also allows more versatility to your build, allowing you to shift around your build order as a specific game situation demands (i.e. I wouldn't finish Randuin's straight out, given the use of HoG for extra gold farm). Try changing it up in a game, grab that second Giant's belt before you polish off Randiun's, stuff like that.

As mentioned previously, Strength of Spirit gives you absolutely zero benefit. You're better off investing in the Haste mastery for the overall improvement on the Ghost spell, and dropping the remaining two points into the offensive tree, on Offensive Mastery or Lethality.

Otherwise, this is a fairly solid build that I intend to try the next time I play Morde. I haven't had much success building him hybrid so far, so might as well try this.

Note : Mordekaiser has NO mana, strength of spirit is totally useless because your max mana is 0. Perseverance may sound good, but good hands is way better taking off over 6 seconds of your death. You got no health-regen spell, so perseverance is not useful (spellvamp/lifesteal does not equate to health-regen probably). Suggestion, get hextech revolver moved earlier so you won't lose hp when you use your skills, frozen mallet/rylai before FoN for boosted regen as well as thicker hp. Randuin's omen's active is slightly less, replaceable by warmog, which gives 1350hp at maxed.
Hope it helps

nice guide but you did waste the hp regen/mana on your masteries you could put that into crit dmg or even good hands but really good

Very informative guide :D