The best replacement for mordekaiser is leblanc.

The best alternatives to mordekaiser are rated as following:
★★★★★  leblanc
★★★★  gragas
★★★  pantheon
★★★  kassadin
★★★  heimerdinger
★★★  katarina
★★  teemo
★★  akali
★★  yasuo
★★  fizz
★★  nidalee
★★  shen
★  nasus
★  shaco
★  gangplank
★  tryndamere
★  anivia
★  sion
★  malphite
★  karthus
★  lux
★  garen
★  mundo
★  vladimir
★  ryze
  blitzcrank
  xin zhao
  yorick

Your alternative for mordekaiser is not listed? Suggest!
Speaking about mordekaiser, one probably shouldn't forget about spell vamp.

Other search terms related to mordekaiser and their ratings are:
★★★★★ spell vamp
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Google Trends

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mordekaiser
leblanc
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