Jeff "Mantas" Dunn

Mantas said he used a Gibson Flying V knockoff on In League with Satan

''I had a Marshall JCM800 and a cabinet I bought second hand by some company I never heard of.''

Those were the earliest years of the JCM800 so that might have been (hardware-wise) a JMP800 with the JCM800 aesthetics (because the early JCM 800 models were the same as the JMP 800 ones).

Jeff "Mantas" Dunn played an Ibanez Roadstar II Series electric guitar during the 1980s, as evidenced by a user-uploaded photo on Ultimate Guitar.

Used this guitar in the middle 80's

Mantas talks about his gear in this article

Jeff "Mantas" Dunn is seen using the Caparison C2-ANG QE guitar in a photo available on Metal-Archives.

Jeff "Mantas" Dunn is seen using the Caparison HORUS-M3 CC electric guitar in a user-uploaded photo on Metalsucks.

can be seen behind him at 32:18

can be seen at 32:51 atop speakers

can be seen in this video behind him

According to Jeff 'Mantas' Dunn's official site, he used a CSL Super Fuzz, and is quoting as saying;

My first distortion pedal, purchased from Jeavons of Newcastle. Essential to the early Venom sound and used throughout the recording of the first two albums.

According to the equipment section on Jeff 'Mantas' Dunn's official site, he uses the Ibanez TS9 Tube Screamer, with the quote as follows;

My primary overdrive pedal, providing the signature boost and mid-range punch that cuts through the mix. Essential for leads and adding harmonic richness to rhythm parts.