Most mechanically intensive combo?

Clicking the thresh lantern in low elo.

Madlife's flash over the wall and hookerino. or Madlife's flash, lantern over the wall, flay, the box.

Mechanically intensive? 1v5 as Yasuo dodging everything with split second dashes.

Azir definitely tops the charts in terms of mechanically intensive.

ryze ult kappa

Jayce's full combo is pretty tough to do

(I know its an anciently old post, but who cares? (sorry anyway)) (I thought it would also funny to see that in all these years, no "mechanic-intensive" champions were released (?))

I'd say the fastest one (requires most clicking coordination) is something like Rakin's Vladimir combo (instant Ehold>F>Erelease>QRW>protobelt>Ignite), that includes using all QWER and both summoner spells in less than half a second, but also demanding timing and holding buttons while pressing others, so it's the hardest to press.

There's also a few Riven one's, but they're probably still easier after all. The hardest ones to perform would be stuff like Lee Sin's (or maybe Riven as above?) Q>ward>WREF>Hydra>QE while insec'ing from side (it's a bit harder to perform from the sides)

Personally, i think Thresh's hook + lantern + flay in air-combo is pretty intense. You have to aim your cursor at two separate players nearly at the same time, and hit them both in under half a second to succeed.