Champions that scale with AD and AP are good.
Believe me, the champions themselves might be problematic little bastards, but the notion that an AP item will never be useless on an AD champion, or vise versa, is always a good thing.
You might have champions that can thrive on full-AP or full-AD builds
, but there are some champions that at least make either stat not completely useless, like Caitlyn's Net Gun, or Kha'Zix's healing.
Funny story about Kha. A long time ago, when Riot first gave his W some AD scaling, they said something along the lines of, "When Kha gets a baron buff, he just has all that AP just lying around! It ain't doing anything, so we're changing that." That was really smart, and I appreciated that! I just think every champion should have that benefit of scaling off of AP, even for just small things. Not too small, though.
