複数のフレームを持つバトルバックイメージをバトルのアニメーションバックグラウンドに使用できます – GALV_AnimatedBattleback.js

Galv's Animated Battlebacks
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In order to make a battleback animated, you need to use specially made
battleback files that contains multiple backgrounds lined up next to each
other and the filename to include in braquets a number of how many frames
are in the image, a comma and then the speed the frames cycle.
Each frame should be the size of your game window dimensions.
(See demo for example).

EXAMPLE:
A battleback with 3 frames and speed 10 would have a filename like:
Forest(3,10).png

Keep in mind that large image sizes can cause loading lag, so you use this
sparingly and maybe get a pre-caching plugin to precache your battlebacks.