Gholdengo

Gholdengo has the huge honor of being Pokemon #1,000, one of the greatest milestones in the entire series. However, that distinction doesn't exactly make it good. Ghost is its only viable attacking type, and it's pretty outclassed on that front. And even if it had a Steel Type moveset, that's another type that has huge competition. It seems that Gholdengo just has no real utility at the moment.

Best PvE Offensive Moveset

• Hex and Shadow Ball is a great Ghost Type moveset, and Gholdengo's best offensive moveset.
• Astonish, Dazzling Gleam, and Focus Blast aren't great options.

Best PvE Defensive Moveset

• Hex is Gholdengo's best defensive Fast Move, easily out-pacing Astonish. 
• Dazzling Gleam is the best overall option on defense, as it comes out fairly early and has great coverage alongside Hex.
• Shadow Ball is objectively good, but it shares a type with Hex, meaning it can easily be walled by Dark or Normal Types
• Focus Blast has perfect coverage with Hex, resisted only by Hisuian Zorua/Zoroark. But its high cost makes it pretty unreliable on defense.

Hex is preferred over Astonish for its higher energy generation to fuel Gholdengo's expensive Charged Attacks. Astonish is also simply awful.

Shadow Ball is Gholdengo's bread and butter STAB attack, being its cheapest Charged Attack and having solid DPE. Focus Blast is extremely expensive, but it has great DPE and offers nigh unresisted damage when combined with Shadow Ball. Dazzling Gleam's coverage also pairs well with Shadow Ball, but it has less DPE and doesn't have as wide of a coverage as Focus Blast does.