I just realized how good Amumu's passive can potentially be.
It reduces the enemy's magic resist by 25 for 3 seconds on-hit in the lategame. This means that this passive alone makes your average marksman without MR investment only 5 MR away from being dealt true damage. Get yourself Sorcerer's Boots, Liandry's, Void Staff, Runes and Masteries on top of that and you will likely deal true damage to them or get their MR value really close to 0 if they have MR runes and maybe a QSS. Only a Banshee's, a GA or a Maw would really save them from it.
Gonna try this tomorrow. Shame I didn't do it with the old Abyssal Scepter.
