Mordekaiser vs Tryndamere

Aim Obliterate (Q) at a lone enemy: if only one enemy is hit, the damage increases.

Hit champions or monsters three times, then stay close: Darkness Rise (passive) then surrounds you with a damage aura and gives you move speed.

Pull your targets into the Obliterate (Q) zone with Death's Grasp (E): each spell that hits also counts toward Darkness Rise (passive).

Cast Indestructible (W) when you're taking damage: it turns stored damage into a shield, and a recast converts part of it into health.

Cast Realm of Death (R) on their carry, or their jungler near an objective: you isolate them with you, steal part of their stats, and keep them if you kill them.

Avoid taking a trade when his Fury is high: with Battle Fury (passive), it raises his critical strike chance, and Bloodlust (Q) turns it into healing.

Hit him when he walks up to minions to farm: each last hit gives him Fury, which Bloodlust (Q) then turns into healing.

Against Mocking Shout (W), back off sideways rather than turning your back on him: the spell only slows enemies who are facing away from him.

Once he hits level 6, plan for what comes after Undying Rage (R): he can't die during the effect, so back off or hold any CC you have, and finish him when it ends.