From the official release announcement - "A dark path, Forsaken Jayce does tread"
"The hammer is the source of the power.
The power is the hammer of the Forsaken.
The Forsaken are the power of the Order.
And the Chosen will crumble.
Break your enemies as Forsaken Jayce, available now in the League of Legends store for 1350 RP (on sale for 975 RP through 23:59 PDT on May 8). Challenge the darkness as Chosen Master Yi, 54% off during Forsaken Jayce’s sale (239 RP through 23:59 PDT on May 8)."
1350 RP (on sale for 975 RP through May 8th)