Twitch

Twitch's scaling plus Yuumi's additional bonuses should make for a good lane, Twitch will have to farm early but a good Yuumi can poke enemies to allow said farm, late game you both scale!

Kai'Sa

Vayne

Vayne is busted enough due to her passive moving faster towards enemies, alongside Yuumi's "Zoomies" you can secure attack speed for vayne and speed her up stacked with her passive for easy picks.

Ashe

Ashe slows, you speed up. Both of you together can create major harrass for the enemy team and cause trouble with Ashe's volley and Yuumi's Q

Draven

Draven works well with Yuumi due to his movement speed plus the additional bonuses Yuumi can grant him, he is strong on his own but with movement speed, heals and his lethality, he can get secured and easy kills.