Hello, I'm not an artist but I hope the UI I propose here will help to design the final UI.
First, I imagined a window like the one above when the fight begins. It offers a team preview with the username of the players fighting each other. The 2 icones on the bottom right corner are designed to host pictures of the command "Run" and "Fight".
This is the basic screen for 1 vs 1 fight. On the top left corner it shows how many turns have been played and a picture of the current weather on the field (with the turns).
Lots of information about the pokemons fighting are displayed : percentage of life, if the pokemon is taunted, seeded etc. , a zone symbolised by a square with a cross inside is planned to host a gif for paralysis, poison, burn and sleep status. Information about increased or descreased stat are also available. The switch part shows the pokemon in the team you can put into the fight.
When you click on BAG you see this.
Then you can choose to use he object on a pokemon of your team.
A click on bag then a pokemon and finally the attatck of the pokemon for which you want to recover PP for example.
When you click on FIELD, it gives you information about entry hasards and the terrain (is there electric terrain, grassy terrain etc.)
When you click on one of the 4 attacks, in the "general window" you will be asked to confirm your attack with mega evo and z-move button.
When you click on a pokemon you want to switch with an other on the field, information about the pokemon are displayed in the "general window". The squares with a cross inside represent the pictures for the "back" and "confirm" option.
This is a view of the 2 vs 2 battle window. The 3 vs 3 battle window is easily obtainable with this screen.
Do not hesitate to ask if you need more details about my Battle UI.