As an early disclaimer, please do not take this build into ranked. It is purely for entertainment, and while it can be pretty strong, I haven't tested it enough or played it as anything more than a meme.

Basically with this build you want to rush sunderer and then abuse the procs. Sometimes your W is more worth getting sunderer off instead of the full shield. Apart from that you just want to hit them a lot. The only real issue is that morde can have a hard time staying on top of his enemies. One thing you could do early is leveling E instead of Q. The main reason I still level Q is because it gives you poke and the cooldown is way shorter, but its up to you if you struggle staying on somebody, as the damage values for your Q don't really matter, and more so just that they count as an ability for sunderer.

This being a hybrid guide, don't expect your abilities to really do anything until you get nashors and lich bane. You could also throw cosmic drive in there if you want the movement speed and ability haste, but the build listed is purely on hit. Guinsoo's isnt necessary but it does help get more bork and nashors damage, as well as lich bane and sunderer if you time it or get lucky, which can be incredibly powerful if you want to pay attention to that. If you get peeled at all, youre probably dead because youre not very tanky and need the lifesteal from bork and sunderer to stay alive. Try to save your ult for when you can't get on anybody. Also space out your abilities to take advantage of sunderer and lich bane. For example, don't E + Q, that combo is useless once you get sunderer. You want to E, auto attack until sunderer is up, Q, aa until sunderer is up, W, sunderer, and so on. Late game your Q is low enough cooldown and you will actually have some AP so the combo still works there.

Apart from that this build is super fun, and seeing morde attack so quickly is pretty funny. You also become pretty strong in a 1v1, which is pretty nice in the top lane.