The Spike Spinner is basically a "revolver-like-nailgun" which came in version 2.3.0, unlocked at level 20, and can be purchased for 96,000 coins. It fires just like a nailgun but only with huge railroad spikes. It's a modified revolver that has a bigger cylinder, making it able to fire its spikes. It also impales your enemies onto the walls like the Impaler.
This can be alternatively obtained by inviting 6 friends by having them enter your Friend Code in the start of the game (account is new), then they must reach level 12 to have a successful invite.