i make stuff

In these two screenshots - the first one is the main GIF which we will be using, the second GIF is the one we want to merge with. Let us begin by dragging our second gif into the main canvas, or alternatively you can duplicate it into your tab.

Now that you have placed your GIF into your main canvas, it's optional to move it but always encouraged - of course, do know that you should only move them in a separate canvas as it may lag if there are multiple of other layers.

Select both/all of your GIF folders and click Layer > Animation > Merge. There will be a tab popping up on the top, warning you about the amount of layers that will be duplicated

Now why does this matter at all? Your canvas size not only affects how much MB/KB it'll take but also the amount of FPS and timeline. The more frames = more MB/KB.

And now your GIFs are now merged! And something to note, do not place all of your GIFs into a single folder, if you do - something like this will pop up.

You have to first merge all your GIFs and later on placed them in a folder if you wish to overlay them with your effects ( Like I did ) Also, when exporting them - if your canvas size is huge, for instance; 1920x1080, something like this would pop up:

If you desire to maintain the canvas, click OK and resize it later on. ( Mind you that it may take long for it to export to that size depending on how huge it would be ) Alternatively, you can also lower the quality in the settings here:

( Ensure that the percentage is not too low! Otherwise it could get quite noisy like my previous works as you can see.. )

And here is my result ;

I hope this would prove to be helpful to you, do please feel free to inquire for anything else - I'd be delighted to assist.