I want to clone Sprite2 four times.

I can do it at least two ways:

repeat (4)
create clone of [Sprite2 v]
end

(or)

create clone of [Sprite2 v]
create clone of [Sprite2 v]
create clone of [Sprite2 v]
create clone of [Sprite2 v]

But the first one takes a few ticks to do and stops the rest of the script from executing until it's finished, while the second one is very inefficient and takes up a lot of space. What is a better way to do it?

is the first one in a no-refresh block or at the top level>?

I'm not sure what you mean by top level, but it's not in a custom block. My code looks like this:

when I receive [startCode v]
code [... v]
repeat (5)
create clone of [Sprite2 v]
end
stop [this script v]

You can see my (embarassing) code I am referring to here: In the Player sprite, at the bottom of the huge ugly gamestart hat block.

ok, well create a custom block that does what the ‘when i receive’ code does, and call that block instead of the lines of code directly. if you mark the custom block as ‘no screen refresh’ I think it may improve your clone creation time. It'll never be instant but it may be a bit faster. Be wary of race conditions when two clones are being created at nearly the same time - copy the clone ID immediately and then use local variables only.