Rammus' Powerball interacting poorly with Quicksilver Sash and Mercurial Scimitar
Mainly for fun, especially for URF. When Rammus uses a QSS it "cleanses" his powerball resulting in him not being able to use Mercurial Scimitar for its 50% movespeed buff. Rammus can use all other movespeed buff items such as Youmuu's and Shurelya's without it cancelling so the source has to be the cleanse portion of Merc Scimi.
IMO Merc Scimi should interact positively with Rammus' Q and let him achieve even greater speeds, this change will barely affect balance if at all and would be purely for fun's sake - which I believe is the most important reason.