This feat has been waiting to be calc for a long time... and here it is.
Skyscraper: 27 px/80 meters
Mountain diameter: 299 px/885.925925926 meters (radius is 442.962962963 meters)
Mountain height: 417 px/1235.55555556 meters
(Pi*442.962962963^2)(1235.55555556/3) is 253878384.884 m^3
2750*253878384.884 is 698165558431 kg to knock down, or Class G.
But thats just the Lifting Strength. Whats more to this is the force to knock it down, or the AP.
(Pi*442.962962963^2) is 616431.330203 m^2
60000000*616431.330203*0.6 is 2.2191528e13 N
885.925925926*2.2191528e13 is 1.966005e16 joules/4.6988647227533464346 megatons, or Small City level+
Huh... much better than how Death Battle did this feat, probably the difference in heights for the skyscraper. Anywho, both Sonic and Metal Sonic could trade blows with each other, and one of them had to have done it.