'Recon' Bob Yewlaiter is a character in Stick RPG 2 that will upgrade your sledgehammer if you have the proper materials. He is found at the 24 Hour Laundromat[1] on the first island.
If the player obtains the Unobtainium[2], or Einsteinium, alongside the Old Weathered Sledgehammer, he will offer to improve it.
The Weathered Sledgehammer will be upgraded to a heavy sledgehammer the first time it is improved. the second time, it will be upgraded to be a Super Sledge