Jay Ingle - lead developer, designer, and artist:
Godot has a neat AnimationPlayer node. It can do just about anything you can imagine. It can even call functions located in other places, so the power is nearly unlimited.
When I first began using Godot, and I needed something to happen at a certain time, I would use a Timer node. Then I would set up an AnimatedSprite2D node for the animations. Let's say I want a hitbox to be enabled at a certain time during an animation. Well we can start the Timer and the animation at the same time, and then when the Timer finishes, we enable the hitbox. Then when the animation finishes, we can start a different timer that will restart the animation.. and restart the other Timer... and hopefully you can see how this quickly becomes complicated, even for something simple. The other problem is that the animation is not exactly tied to when the hitbox is enabled. It SHOULD be synchronized, and if I have set my Timers correctly, and animations are a certain length, then things will be synchronized, but will very easily break. Any change to any component will destroy the timing. AnimationPlayer nodes remove all the guesswork, and tie things together real nice.
Above, we have added sprite frames from a Sprite2D node, and we call functions enable_hitbox() and disable_hitbox() at specific times. We have a nice visual where we can see which frame is shown at the time of those function calls. We could easily set this to loop, but at the end of that timeline I am calling start_timer(), which is how long until we restart this animation again, because I want a little more control of how long the flame is inactive.
Here we can see that you can even keyframe aspects of a particle system. We can change colors, increase or decrease amount of particles, and many other things.
If you are new to Godot, and you are using AnimatedSprite nodes, I would advise switching everything to Sprite node plus AnimationPlayer instead. Especially if you are not too familiar with animations and keyframes in general. AnimatedSprite nodes are very simple, very basic, and do their job well, but AnimationPlayer nodes are much more powerful, and will save you a lot of time and effort. Let them do the heavy lifting!