Full Cooldown Rate Thor:
This build might not seem that unorthodox at first, but it uses some very strange items that you don't normally see on Thor.
The build:
Bumba's Hammer (Starter)
Jotunn's Revenge
Tekko Kagi
Pendulum Blade
The Crusher
Chronos Pendant
Staff of Myrddin
This build achieves 120 base cooldown rate (with Tekko Kagi stacked) which is equivalent to 55% cooldown reduction already, but the real nonsense starts to happen when you factor in all the flat cooldown reductions in the build.
Bumba's Hammer gives 1s flat off ALL cooldowns when you AA cancel (which Thor does A LOT)
Jotunn's Revenge gives 1s flat off basic cooldowns and 5s off your Ultimate on getting a kill
Pendulum Blade instantly reduces all active cooldowns by 3s on a 50s cooldown.
Chronos Pendant gives 1s off ALL cooldowns every 10s
Staff of Myrrdin lets you double-cast any basic ability every 150s
Since flat cooldown reductions are more powerful the lower your base cooldowns are, you get a tonne of value out of these effects.
With a build like this, Thor's 3 has a base cooldown of around 4.5s and by the time the animation completes, it's more like 3s so Pendulum Blade basically lets you double-cast it.
You can also double-cast Thor's hammer (1) in his combos using Staff of Myrddin for some insane damage.
Since Thor's Strength scalings aren't massive, you still do a good amount of damage with a build like this just by purely working off base damage and item procs from The Crusher and Bumba's Hammer.
It's a very weird build though, with 2 items being purely intelligence which Thor makes 0 use out of, but it's for sure a fun build to use as you almost always have an ability up no matter the circumstances.