According to Boss' diagram, Malmsteen uses the Boss OC-2 octave pedal.

He uses two Boss OC-2 octave pedals.

Pino is featured in Bass Player magazine where the Boss OC-2 is listed as one of his standard session tools.

A photograph of Jaco Pastorius's rig from his 1986 tour in Italy clearly shows three Boss pedals, one of which is identified as the Boss OC-2 Octaver. This image serves as evidence that Jaco Pastorius used the Boss OC-2 Octaver during that period.

A Boss OC-2 Octave Pedal appears in Mike Einziger's pedalboard at the start of this rig rundown video.

Pictured on Gallagher's official website's "Effects / Pedals" page and mentioned in an interview in an August 1991 Guitar for the Practicing Musician interview with Vivian Campbell.

VIVIAN: You get a tremendous tone for a single-coil Strat. Are you using any kind of distortion device between the guitar and the amp?

RORY: I've got a Boss Graphic EQ.

VIVIAN: Is that a little 6 band?

RORY: Yeah, one of the real old green ones. And I've got a DOD analog. They're back on the amps, and that's set at the minimum setting, just for a little bit of slap-back. I've got a Dyna-comp, which is on all the time, to drive the songs from the leads. It's not for effect. It's a form of compression and I have it at a setting where the compression's really low on it. I usually use a Tube Screamer, which broke down on me. Last night I was using a Boss overdrive. I use them for some solos, not all solos. I was against using them for years. If I was doing a solo, I had to look at the monitor guy to turn it up and all this. So I keep close to the natural sound. I have a brown Boss octave thing.

VIVIAN: I heard that last night. You sounded like Prince! He uses that a lot.

RORY: I've got a Boss flanger, as opposed to a chorus, which I use sparingly, I use that only in “Shadow Play” and “Moon Child,” and one other song. That's my talk on technology. I have a Vox wah-wah which I did use for one or two gigs, but purely to click it on for slide solos. I used it in the studio, for some solos as well. I don't use it on-stage, because even as it is, I try to keep it simple, within reason.

munky says in an interview Head used the Boss OC-2 in Here To Stay

From the interview with Premier Guitar:

What effects did you use for Blood In, Blood Out? Holt: I use a ton of different pedals. I love stompboxes—they’re like crack to me! I have pedals from Maxon, Dunlop, HomeBrew Electronics, Pigtronix. I use a lot of the Maxon Tube Screamer-type pedals. They made the original ones, so they have ones that are exactly like the original, sought-after ones, and they also have updated versions.

I also love the Boss Octaver. I’ve never been without one my whole life. Dunlop makes a bass octave pedal, which sounds probably even a little better and has a smaller footprint, which I also like. And I use a Voodoo Lab Ground Control. With Slayer, I’ve been using the Dunlop Jerry Cantrell wah. Kerry [King] uses the Zakk Wylde wah, so I wanted something to differentiate our wah sounds.

Here in this webpage it shows pictures of Jerry on stage with pedals behind him on his racks 3rd photo down shows his mid-late 80s early 90s pedal rig with the boss oc-2 octave pedal.

"You said you don’t really hear effects, but you did use some stompboxes on the album—right? I don’t need any overdrive pedals because the amps have plenty of overdrive. But I used a CryBaby wah, a Dunlop JD-45 Rotovibe, a Dunlop TS1 Tremolo, a Boss OC-2 Octave, and a Mesa/Boogie Revolver rotating-speaker cabinet."

Dave Navarro is noted for using the Boss OC-2 Octaver, as detailed in the "Dave Navarro Guitar Setup And Rig Rundown" on Youtube Music Sucks.

In interview with Music Radar, Bettencourt says about his OC-2...

"There are songs like Comfortably Dumb and stuff off of [2008 album] Saudades De Rock, or whatever, that I’ll use it for if the songs were written that way.”