I've spent the past week trying to sort out how to do this using Dragonbones and I've got a way that finally works great, but it will take you a bit of learning the free Dragonbones software if interested. Also, this is not the best way to create from an existing spritesheet: You'll want to only use this method for animation that has every frame exported as PNG, or puppet animation.
You'll need to follow some instructions on how to get DragonBones working with RMMV that includes adding some libs files and editing the index.html. These were fairly straight-forward for me.
On to DB - Luckily, you wont need to learn armature stuff for exported PNG, just follow some steps after downloading and opening DragonBones:
When creating a new file, I pick Armature just because it's the safest option, movie clip likely wont work and I don't know the other option: If at any time you can't perform an action mentioned, check the top left of the screen and make sure you're set to Armature. If it's in Animation, you wont be able to move around objects in the Library.
The Armature mode is what you will see by default if you have no animation. So if you have a character visible in Armature, every single animation will have that character visible by default. If you scale up a bone in Armature mode, you'll scale up that bone for every animation. If you make an image invisible and an animation hasn't explicitly set a key to make the image visible, it will be invisible for that animation.
SAVE OFTEN - Program is somewhat prone to crashing, particularly when importing.
1. Create a bone (top right of the screen, a little pointer icon)
1a. Create a Slot (same button as bone) and drag/drop it in that bone
2. Import your animation PNGs to library using File > Import Assets to Library: Choose Duplicate library if you like, this will make a duplicated folder named library that is int he same folder as the saved file.
3. This will create a 'Slot' and 'attachment'. The 'slot' acts like a folder for the image (attachment) so drag any images related to an animation in those separate slots and put them all into one slot.
4. Time to 'animate'! : Swap to Animation mode using the button in top left of the stage. Now you can alter the timeline. The timeline is where you will hide or show which image will be displayed on which frame. First time you're in this mode, you'll want to turn on "Auto Key" (Icon is a little flag with an A). This will key any changes you make. Expand the bone/slot to see all your images and press the circle next to the image to hide or show them. Only one image can be visible at a time PER SLOT. If you want more than one image visible at the same time, create a new slot for the image.
5. When you have all your images in the frames you want, name your animation (it can be anything using alphanumeric characters BUT no spaces, use underscore if you have to) and this is what will be called by the Action Sequencing.
6. At the top right in the library, it will show as "Armature" by default, double-click this to change the name to your character/monster. Again, no spaces in the name. Save your project if you haven't.
7. Now you can export your project. Choose File > Export. By default, you'll be in the Animation Data + Texture tab. This is the one you want. Below are the settings to double-check. Anything not mentioned are default settings that you can leave alone.
7a. Data Config Type: DragonBones JSON
Data Version: 5.0
Image type: Texture Atlas ----go into Settings--> and make sure you have "Power of Two" and "Square" on. Beware that as you add more images for more animations later, with Auto Size on, this may toggle Square to be off as the export adjusts the texture size. Always make sure Square is ON.
Mobile games should aim to be no bigger than 1024x1024 and computer games should be no bigger than 2048x2048. These dimensions I haven't confirmed personally as problematic, but my previous game job had this limit and so have other people on this board. Since the next size up is 4096 x 4096, I'm inclined to believe RPG maker might have trouble there.
At this point, it's a matter of going into RPG Maker (with the appropriate Yanfly Action Sequencing addons and pre-requisite engines) following the notetag suggestions for Dragonbones. In the Enemies tab, you will want to point to the Battler that has the same name as the 'Armature' you renamed in step 6.
Lets say the enemy armature is "Slime", and the animations you included are 'hit' and 'attack' - you'd have a tab like this:
<DragonBone Settings>
Battler: Slime
Replace Sprite
Ani Attack: attack
Ani Hit: hit
Ani Backflip: hit
</DragonBone Settings>
The word after Ani is for Yanfly's Action Sequence to use as an identifier. The word after the : is in relation to the animation name in DragonBones.
This will allow you to use the ActSeq command:
animation backflip: target
to cause the target to play the animation assigned to 'backflip'. Currently it's hit, but maybe later you'll want to create a backflip anim. Include it in DB, name it appropriately, export (re-check that Square is ON). Ani Backflip: hit to Ani Backflip: backflip.
I chose 'backflip' to show that you can apply any animation in DB to any random name for the ActSeq plugin.
Other than all that, just make sure you follow the setup tips in KELYEP_DragonBones docs and vids and set the Preload Assets to ON in the Plugin manager. There looks like a lot here but it works like a charm and the only worries you will have about sprite sizes and animations will be if all your anims will fit in your DB export and battle load speed.
OH also, regarding animation loops (like a forever repeating idle animation), you have to set this inside DB. With the Animation tab active, look at the 'Play Times:' number in the bottom right. Set to 0 for infinite looping, and any other number for that many plays.
That's all I know about it, but it's an option. Good luck!