Scratch always lags when simply using a “repeat (x) next costume” script. this happens the first one or two times the animation plays, and then runs smoothly on the third. This is quite a problem when you need to sync animations to music, or have them play as a jumpscare etc., as it completely desyncs the animation or gameplay respectively. It's nothing to do with bad hardware on my end as It still happens when played on a fairly powerful PC.

Any tips/advice on reducing lag (that doesn't involve a loading screen) would be appreciated

You could use a script that uses a timer when switching costumes such as this one:

when green flag clicked
reset timer
forever
switch costume to (([floor v] of ((timer) * (10))::operators) + (1))
end

just play it on turbowarp i guess, scratch is notoriously slow but the turbowarp compiler makes projects run smoothly

BobaFatL wrote:

You could use a script that uses a timer when switching costumes such as this one:

when green flag clicked
reset timer
forever
switch costume to (([floor v] of ((timer) * (10))::operators) + (1))
end

Timer blocks can be used for different purposes.