The two nerfs from Patch 1.13 -- increasing Lee Sin's mana cost from 4 to 5 and Make it Rain's cost from 2 to 3 -- were accidentally reverted and are currently live. Riot has confirmed in Reddit, Discord, and Twitter that they are aware of the mistake and hope to revert the change today.

Quote From A Small Man

Hey folks, this morning we accidentally reverted some changes we made last patch to Make it Rain & Lee Sin – we should be deploying a fix within the next hour or two.