I'm looking to develop a 2D multiplayer RPG game for Android, with a bird's eye view similar to that of zelda/pokemon. The game is very simple in all ways since my intent is for thousands of players to occupy the same world which I imagine requires good performance. However, I am unsure about the performance requirements of two properties:

1. the tile map that is used as a background is dynamic (interactive). For example, a player steps in the water, and the water turns black. Every tile in the game does this.

2. the tile map is the same object used for all players, but it is displayed differently on each user's mobile device, even though the players exist in the same world. For example, the water that turned black is displayed as red on all other players' screens.

I have knowledge of java, but almost none regarding game dev. tools. Is there a best process for these requirements? Should I develop in pure java, or use some tool like Slick2D etc.? How performance intensive are these properties, if even possible?

Edit: There are no collisions in the game or difficult animations, I am imagining simply changing the colors of the tiles (like in the examples), and a client-server architecture