ADCs should have more items with actives(geared to them), these popped into my head.

-Active: 15% improvement to every stat for 3 seconds if 2 or more enemies are within 800 units of you. AA used at a range of 300 units or more from target refreashes the duration. 200 second cool down.

The obvious conterplay being you need to either get away for 3 seconds or be on top of them as their target for 3 seconds if you need the effect to end. The range stipulation is necessary to prevent things like Yasuo, Irelia, Jax, ect from abusing it too harshly as they dont really need it to be able to 1v2-3 alot of other champions effectively. Full effectiveness would be highly skill based as plenty of champions could ruin the effect easily. Also the marksman would have a 3 second window and anywhere from 200-350 unit window to work within to make it last. My concern is if there where too many mages that could abuse this like lux who likes to auto or maybe Azir as well and i cant think of a fair way to balance around that, maybe exclude AP damage as an improved stat? Also being a ADC item it would have base stats less favorable to them already.

-Passive: Build stacks from autoing to a cap of 100, each stack grants .25% attack speed. Active: At 50 minimum consume stacks to get an equal % attack speed bonus for 3 seconds. If the first auto lands at a range of 450+ from champion and hits an enemy champion then the effect lasts 6 seconds, grants 50% of stacks as movement speed, and the first AA does 50-150% the stacks as bonus on hit magic damage.

Champions that can close the distance before the first auto lands would not have too much of an issue with this Active as the effect would be the very minimum then. Again I made a range requirement for full effect to prevent abuse from unintended champions and so its skill based for a marksman.

-Passive: health gained from life steal is converted to on hit magic damage to a cap of 25. Active: For 3 seconds convert current missing health into attack speed, .25% times as much for each % exceeding attack speed cap. On hit magic dmg is doubled from the passive and the on hit dmg done is healed back. User will recieve half as much benifit from from the active if they are under their own effects of invulnerability to damage, their own sheild, or have not been damaged by enemy champions/epic monsters for the past three seconds before activation.

I just think its an interesting way to deal bonus dmg. The downsides being in place to prevent abuse from yasuo and tryndamere. Really is meant to be a last resort for an ADC that got jumped on.