A pretty rare pedal - the only one I can see for sale in the UK.  Only seems to be missing the sticker from the box. 

Spaceman Effects Mercury IV Harmonic Booster – Rare Collector/Player Grade Overdrive/Boost

The Ultimate Tone Masseuse and Provocateur—Hard to Find, Harder to Part With.

Up for sale is a pedal that needs very little introduction for tone chasers, but is famously difficult to actually track down: the Spaceman Effects Mercury IV Harmonic Booster.

Spaceman pedals occupy a rare tier in the gear world, blending aviation-spec, aerospace-grade physical heft with boutique analog artistry that instantly commands high demand and fierce loyalty on the secondhand market. Units in this condition simply do not pop up every day.

Why the Mercury IV is Legendary:

• Transformative Tone Shaping: As Premier Guitar noted in their glowing review, the Mercury IV acts as both a delicate "tone masseuse" and a powerful "provocateur". It injects your entire rig with air, dimension, and living, breathing overtones that make single notes feel startlingly alive.
• Massive Headroom & Interaction: Offering up to 35 dB of extra kick via the intuitive boost knob, the pedal features highly sensitive, interactive EQ toggles (high and low emphasis points) and a gorgeous harmonics controlthat animates your upper-mid spectrum.
• Studio-Grade Build Quality: Housed in an aerospace-inspired enclosure featuring an engraved metal panel and glowing jewel lamp that evokes '60s outboard studio gear. Inside, it’s a work of art.

Performance & Pairing:

Whether you run it into a clean, high-headroom monster amp to give it an aggressive, oxygenated, and combustible voice, or use it to massage mid-forward overdrives and push fuzz pedals to explosive, edge-of-feedback extremes, it fundamentally improves everything it touches. It is rare to find a device that can so seamlessly streamline a crowded pedalboard while dramatically elevating your core sound.

Condition & Details:

• Scarcity: Highly collectible and rarely seen on the open market. Built in limited runs for players who demand uncompromising boutique quality.
• Cosmetic/Functional: [Insert your specific notes here, e.g., Mint / Excellent condition, home-use only, velcro on bottom, fully tested and 100% operational].
• Included: [Original box, swag, certificate—if applicable].

Grab a piece of elite boutique engineering that rarely stays available for long. Ships securely packaged via tracked and insured mail.

From Spaceman Effects:

About Mercury IV 

We are excited to present the Mercury IV, a unique Germanium Harmonic Boost pedal. Eight years ago, we introduced the Mercury III and we have updated the original circuit for a new spin on that classic pedal.

The Mercury IV is a dynamic tone enhancer, created to bring out additional harmonic character from instruments and amplifiers. The pedal features a unique, discrete analog circuit, with a meticulously selected vintage germanium transistor at its heart.

The Boost control of the Mercury IV offers a staggering 35 dB of gain, with nine (9) tone-shaping options via two toggle switches, to gently or aggressively boost tube amplifiers. The real magic however, resides in the Harmonics control; bringing more dimension and life to ones’ tone. Subtle sparkle, complex textures, and octave-like overtones can all be found here. With a sound and response like hot tubes on the edge of breakup, these even-order harmonics are independently generated, giving you full control over the mix.

The Mercury IV is completely hand-soldered and handmade in Portland Oregon to the highest degree of quality possible. These are truly artisan-crafted tone devices, sparing no detail within or without. The Mercury IV utilizes true-bypass switching via the heaviest duty mechanical footswitch available, while your tone is transferred via quality open-frame Switchcraft jacks. Open one up and you’ll see an unparalleled display of craftsmanship; with immaculate hand-soldered PCB, detailed military-spec wiring, and custom Spaceman heavy-duty battery connector. On top of the cast aluminum enclosure sits a durable, engraved vinyl faceplate and jewel indicator light. This pedal is truly built to last a lifetime.

Each pedal number is hand-hammered on the nameplate, stating its limited availability and each is also signed and numbered on the inside.