Crash Bandicoot N. Sane Trilogy

You need to unlock all 25 Crystals, all 45 Gems and all 30 Gold Relics. On the pause menu, it should show that you're at 100% complete or more

EDIT: You can unlock this anywhere over 100% completion, as HALO3KIRBY and ReaperOfBurgers have mentioned in the comments.

After collecting all the required items, reload Toad Village (level 1). Around halfway through the level, you'll come across a checkpoint box on the floor in front of a log with three other boxes on top (two standard boxes each side and the middle one with a "?"). Just beyond here is a toad enemy hopping through a puddle.
From here, look to the right and you'll see a gate leading to a small house with a fake version of Crash dancing near the doorway. Hop up onto he ledge in front of the house, aim your Fruit Cannon at the fake Crash then fire at him a couple of times.
This should pop the achievement.

If you're stuck on 42 Gems, you'll likely have to get the two hidden levels, each have which have their own related achievements. One of the hidden levels is in Dino Might (Level 11), where one of the pterodactyls flies into you, see the full solutions here:


And the other is in Road Crash (Level 14), where you need to drive into an Alien Crossing sign on the left of the track after the third diner. Solution for this here:


If you're struggling with the last Gem, once you've unlocked all gold relics, a final gem will appear in the centre of the Time Twister.

You need to unlock all 42 Gems.
In level 1 fire in Fake Crash.

I just got this achievement and I’m only at 54% as it turns out of you know the place where he is you can just shoot there and the achievements will pop up. I just shot the house a couple of times and it pinged hope this helps

Fake Crash can also be found at the end of the Death Route in the Future Tense Level (Level 31) on a ledge at the right hand side just before getting back on the Death Route platform.

I realise this is a lot harder than the above solutions but I thought I'd mention it as it means Fake Crash can be found on more than 1 level.

To unlock this achievement, you must complete the game at 104%, obtaining all the gems and relics, then you have to shoot Fake Crash in level 1 (Toad Village) with the bazooka.