Thank you, sir. I'm just venting my frustration from everyone complaining about EVERY new champion (except Bard). Sorry if I sounded a little rude up there.
If you wanna learn Morde, just play him non-stop for awhile. He's actually a very simple champion, and pretty easy to learn. One of the biggest things to learn about him if you're using quickcast, which you should be doing, is the range of his E. If you can learn the range of that, then you can poke an enemy in lane and last hit specific minions without pushing your lane too quickly. Most of the time, you'll be pushing your lane without even trying though, so always ward up. Upgrade your trinket ASAP. Mordekaiser is weak against ganks, so get that trinket whenever you can, and always, even if you think you need that gold, buy wards. WARDS! Ok? Ok :D
Besides that, Mordekaiser doesn't scale as well as most Mages with AP, because his ratios aren't that great.
Get that Hextech first > get some boots early > if you're against someone squishy, and you're doing well, get Luden's. Funny thing about Luden's with Mordekaiser that has secured me manyyyyyy kills when they run away (this may not work since they nerfed Luden's). When you ult someone, and they manage to use all of their mobility/CC and whatever to get away, spin in circles, YES CIRCLES, and spam your skills randomly into the air (DON'T HIT ANYTHING WITH THESE SKILLS). This will charge up Luden's, and each time it hits 100, Luden's will proc from anywhere on the map from whoever was ulted and hurt them even more. It works, and it's an amazing way to counter that evil potion they drink.
Besides that, my normal build ends up:
(if against AP team or mid)
(if their AD champs are bugging you)
and if you ever get a huge lead and get fed, get
. Yes, he doesn't scale very well with high amounts of AP, but his ultimate will take about 50-60% of their HP lategame with this. So take it if ahead ;)
If you have any other questions, feel free to ask!