AD casters
(Referring to ADC casters) I have been noticing tanks are pretty strong in solo queue lately and building an early botrk seems to be the best approach for adc's. But some adc's are just not good with it as an early item, such as cait. This gave me the idea of a new item that might bring some other AD casters back into the game a bit. (I don't watch much competitive play, maybe AD casters are currently pretty balanced. This is based off my solo queue experience). One possibility:
60-100 attack damage Passive: Grants 15% of your bonus ad as flat armor pen. (15% would probably be op, but you get the idea)
If you had 200 bonus ad, you would have 30 additional armor pen.
or: 60-100 attack damage Passive: Grants 5% of your bonus ad as additional armor pen.
If you had 200 bonus ad, you would have 10% armor pen.
(graves might need to be nerfed first)
Edit: Everyone seems to think it would be OP, do some math first, you will find it wouldn't be good, unless you had some heavy ad to back it up. It would add some diversity and make 'some' champions "better/different".
Edit: I wonder if it was even worth posting on this site. 90% of the people who replied were answered with a quote from my post, meaning they either didn't bother to read it, or just didn't understand...