Tony Stark's Hulkbuster armor first appeared in Iron Man (1968) #304, written by Len Kaminski with art by Kevin Hopgood and Steve Mitchell, as part of 1994's Crash & Burn storyline. First suiting up in the armor in preparation of facing Hulk, the specially designed rig replicated Hulk's size and strength while also adding advanced weaponry. It placed Tony and Hulk on an equal level the first time they faced off, and the suit has gone through multiple upgrades since then, including one which gave the Hulkbuster power from a Celestial.
The 2020 variant cover of Immortal Hulk #28, with art by Dale Known and Jason Keith, gives the Hulk a steampunk makeover that more than merits a Hulkbuster designation. This variant cover was one of many to celebrate the arrival of Iron Man 2020, giving each character an Iron Man-style redesign. Hulk's new look centers around a clockwork aesthetic, and the spikes that encircle his arms, the sharp points of the gears, and the mechanical weaponry make Hulk more deadly than ever before.
Hulk's strength is already so potent that there's not much armor could do to enhance it. However, this suit does give him the offensive capabilities that he lacks. It takes full advantage of Hulk's pre-existing strength and combines that with spiked elements that will surely only improve Hulk's destructive abilities. Additionally, the deadly cannon that sits on his shoulder adds a long-range element to Hulk's attack that he hasn't previously possessed. Judging from Hulk's new mechanical eye and the lack of a visible trigger, this cannon is keyed directly into Hulk's brain and can cause immeasurable destruction with just a single thought. This redesign changed the concept of 'Hulkbuster' from a suit used to defeat Hulk into a suit used by Hulk to help him to defeat others.
Although Marvel Comics unfortunately never showed Hulk's Hulkbuster armor in action, the concept was more than enough to keep fans intrigued. Perhaps in Marvel's new Mech Strike series, Hulk will be able to showcase his abilities combined with technology and give readers a taste of what this armor could have been.