I am De****0 professional gold rank league of legends player who gets paid the big bucks to main top and jungle.
I have mained top for 2 seasons now and believe I have a grasp on what to do in the "boring" lane. Morde is one of my top champs and gets an incredible amount of work done. However he does take some getting used to as he is very clunky
Despite all this Morde is very fun and efficient at winning, but not always carrying games. He can carry a fight if left alone to wreak havoc, but that never happens.
His real power is in his pushing potential, Morde can clear very fast and with his ghost pals he can sweep a lane or turn a post-fight situation into a 4v6.

Ok so hears the deal. Morde doesn't work and that's why he is so great. His W's sustain is nuts and when it's up he can constantly charge his shield. The longer one fights Morde the worse the situation gets. His Q starts off as good sustained damage but later becomes very bursty. His E keeps him alive and does solid damage. Morde does best in 1v1's inside of minions waves or giant teamfights (Especially around objectives). Morde is at his strongest with a few friends at his side and his ghost buddy is by far the most effective. Morde with a ghost is far more powerful than without, as it obviously gives him a W target it also charges his shield and steals health thanks to gunblade. Morde is very weak to being caught out so try to travel in a pack. Being positioned in a team fight is also very important, try to stay away from the major bursts, but at the same time be constantly doing damage to keep your shield up. Morde can be bursted, just like everyone else.
However Morde's crown jewel of teamfighting is his ult. the healing from it can revitalize you during a fight and the ghost it spawns gives you and immense boost in power. Not only does it give you an extra teammate it also gives you bonus health and AP(based on the targets). Ghosts also copy whatever passives the original had, this includes items.

If your jungler wants to cheese an early dragon follow him.
Morde's early game is like a baby's first steps CRUCIAL
Poke hard with your E and shove/heal with your W. Morde is very weak to ganks due to his lack of mobility so ward often and keep and eye glued to the map. Early fights and trades are easy, stand in a minion wave with your W to soak up shielding and health. Your Q can be used to farm under tower of be charged on minions and comboed with flash for surprising burst. Ult doesn't do as much damage as you would expect so save it for closing off kills.

Snatch up towers when you can and always be responsive to dragons. Push with a friend, either a Ghost from the ult or the jungler. Morde has excellent pushing power, make use of it. Looking for minor scraps is a good way to pick up a ghost buddy, get some quick gold, or setup for drag.
Morde is the botlaners best friend around this time, pick up a pet dragon and roam bot to stomp the lane.

Stick with your team at all times and ALWAYS be looking for dragon. Don't pick fights or engage unless you have someone who can on your team (i.E malphite) Morde has excellent responses to engage. Wait for someone to start the fight and dominate it.
If you have flash up charge Q on the tanks then flash into the squishiest guy(Usually ADC) and bust them up with Q+R

Does fairly well outside the few listed above

Gunblade's healing is crucial, rylais and liandrys synergize very well, but outside of that try whatever you think could work.

I typically pick Morde mid if i see a Zed or Yasuo because with exhaust Morde makes these clowns suffer, he doesn't have great matchups against most of the mages mid but against all melee mids he causes extreme distress, just be sure to have exhausts.

Tp is very important as it allows you to get to dragon easier, and a pet dragon is a demolished lane.
Exhaust against the fellas of mid lane is the instant "win fight" button.
ignite kind sucks as of late, but use it if you need some kill pressure