I don't know what I am doing wrong.
I overwrite Game_Character update, added character_animation method to the Interpreter and unique_frame_delays to Game_Character.
Initialized the new attributes and called the method from the map like this: character_animation(-1, [4, 4, 4, 4, 4]) // I'm using a 5 frame charset
And of course I changed "HOWEVER_MANY_FRAMES_YOUR_GRAPHIC_IS" to 5 to test it.
But the game got frozen...
BTW, thank you for your help!