Thunder Shield Challenge is the second Challenge Act of City Escape Act 1 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the Dreamcast era and is playable only as Classic Sonic.
This Act takes place in a heavily modified section of City Escape Act 1, with pillars and obstacles forming new paths that must be traversed with the Thunder Shield.
In this Challenge Act, is given a monitor containing the Thunder Shield, which they need to use to get through the Challenge Act within the given time limit.
The Act begins on a building in the background just beyond the normal beginning of the stage. The player must utilize the Thunder Shield in order to scale the large gaps between platforms, jump over long rows of spikes, dive in between obstacles, and bypass the many electric hazards throughout the Act. The player will otherwise continue through the Act as normal, defeating enemies in their way before reaching the Goal Plate in the section where the GUN Truck would drive alongside the player's pathway.