League of Legends (LoL) Question: Frozen mallet on Nasus?

It can work, but your Wither works rather well at slowing the enemy's attack speed and movement speed. At that rate, Wither out performs Frozen Mallet because the enemy should be slowed to the point where your Siphoning Strike will stack the enemy. If you want more slow potential, I prefer Iceborn Gaunlet. It also provides CDR for more Siphoning Strikes.

You're much better off buying CDR for repeated casts of Wither. Slows don't stack at all (it just takes the highest slow value) so you aren't getting any benefit from the Frozen Mallet proc whenever your target is Withered.

It could work but I think its quite risky. Nasus already has slows so I don't think you would need mallet.

Probably not, but it might work.

If we're talking slows, Nasus can rely on Wither for most of the chasing until your target is dead, which would render mallet's slow practically useless since it won't work for teamfights either with Nasus.

Also the high hp isn't that useful since Nasus relies on resistances to amplify his lifesteal value.

It's already a pretty niche item afaik, so I don't see it working on a champion that won't exploit it unless it was imbalanced in the first place (idk if it is op by stats, passive or price, which is why I said it might work).