O.K. I want to be very clear. I'm not advocating this for a normal team comp. I'm not even advocating you do it often. What I am saying is that if you know how to last hit with Rammus, and see a 4 or even 3 AD team, he works. And with so many people playing Garen or Darius top, Yasou or Zed mid, and taking Yi or Xin Zhao jungle, and they are guranteed to have a "real" ADC - that this Rammus set up and build will shred that team composition.

Rammus doesn't pair well with a tank support like Alistar or Braum. Braum keeps damage off an ADC, and Rammus doesn't need that. A good stun or snare with high AP does best - Lux or Morgana being ideal, but you COULD go with Taric, and then you will be able to use both ults to shred through any armor.

OK - BUT ADC RAMMUS doesn't do enough damage. Well, he does, and more importantly, he doesn't die, and it hurts everyone to attack him. That being said, if you have a jungler that is low damage, and a midlaner that is tanky, and a top laner that is made for sustain, you might have to go with something else like a ravenous hydra to get damage done during team fights.