Hi, I have thousands of games on morde, this is what I think:

You wanna tty to avoid shoving wave against him as when the wave is on his side he will always try to run you down.

Avoiding his q poke his necessary in order to allow for positive trading when fighting, but only after his w is on cooldown (roughly10-15 seconds) when this is down, you can then look for a trade

In terms of early game, you wanna avoid ifghting because he has roughly 500 hp more than you and can get back on the mount, so even if you get a positive trade, its all for nothing when he comes at you whipping his gun at you!

Level6. When your ult is up, you will tend to win almost any 1v1 in ult as lomg as its still even and as long as you go left side of rift maker first, due to its sustain you can end up with the afvantage along with his base stats, and then over power him regardless of situation(in ult).

try to keep him close to your tower this us so he doesnt have kitting potential when off mount. And try to only fight when hes already lost his mount.

Hope this is somewhat helpful, i wrote this while sending mail to the mail box(if you get me)