If you need help with your gallery on the previous sprite which can go previously. Try this code!

when this sprite clicked
switch costume to [((costume [number v]) - (1)) v]

Scratch doesn’t have a built-in “previous costume” block, so we use math (current costume number - 1) to achieve this. And there are many way to do ti. Have fun.

when [right arrow v] key pressed
next costume

when [left arrow v] key pressed
switch costume to ((costume #) - (1))

when [left arrow v] key pressed
switch costume to ((((costume #) - (1)) + (total costumes)) mod (total costumes))

when green flag clicked
forever
  if <key [right arrow v] pressed?> then
    next costume
  end
  if <key [left arrow v] pressed?> then
    switch costume to ((((costume #) - (1)) mod (3)) // Replace 3 with your total costumes
  end
end

when [space v] key pressed
repeat (4)
  next costume
  wait (0.2) seconds
end

Guides aren't really made here, as we already have enough. Also, the suggestions forum has a workaround guide.

tidelgl wrote:

Scratch doesn’t have a built-in “previous costume” block, so we use math (current costume number - 1) to achieve this. And there are many way to do ti. Have fun.

This was already said, but the blocks are broken, so it is confusing.

tidelgl wrote:

Scratch doesn’t have a built-in “previous costume” block, so we use math (current costume number - 1) to achieve this. And there are many way to do ti. Have fun.

when green flag clicked
forever
  if <key [right arrow v] pressed?> then
    next costume
  end
  if <key [left arrow v] pressed?> then
    switch costume to ((((costume #) - (1)) mod (3)) // Replace 3 with your total costumes
  end
end

You don't have to do the mod (3) part, as going to the “0th costume” goes to the last costume

Hello! It's great that you want to help out other Scratchers. However, I think we have enough guides in the forums at the moment. Please feel free to welcome new Scratchers on the group welcoming topic or on individual topics created by New Scratchers.

Other places that can always use more helpful Scratchers like you, are the “”Help With Scripts“” and “”Questions About Scratch“” areas - please use them as designed, by responding to topics created by folks with problems to solve

Finally, a really good place for Scratch guides is the Scratch Wiki - check it out and see if it's something you might like to work on. They have a number of guides - and great organization.