Battleground is a minigame.
The goal is to kill other mice and be the last mouse standing. Mice are vulnerable to hits and falls. Getting shot, falling off, or crashing against a wall will all result in death.
Weapons are divided into tiers. Categories you have to unlock to be able to buy the weapons. You unlock the next tier by getting the required mastery points. You can get those points from any weapon on any tier (not necessarily your current tier).
There are 7 tiers, namely: E, D, C, B, A, S, and the mysterious ? tier.
The final tier requires you to master every weapon in the game from the other tiers.
Weapons of a higher tier are usually better than the ones from a lower tier. But you can level up some weapons to the point where they exceed the stats and usefulness from its original tier.
Every time you use a weapon in a round you will be rewarded with mastery points. Weapons level up by collecting enough points, getting an upgrade on some of their stats.
When a weapon reaches its maximum level, it means you've mastered it. You don't need to master a weapon in order to progress. You can choose to buy better weapons or to keep leveling up the ones you have.
You get mastery points by meeting one or more of the following requirements:
- +1 point on each weapon just for playing the round
- +5 points on each weapon for winning the round (last mouse standing)
- +1 point on each weapon if you win with all 3 lives remaining
- +1 point on each weapon if you're in the podium (last 3 mice to die)
- +2 point on a weapon if you used 25% of its ammo
- +2 point on that weapon if you are in the top half players (last 50% to die)
You also have to meet these general requirements:
- Playing the round - i.e. not AFK-dying
- Having 5 people in the room playing that round (again, not AFK-dying)
- The most mastery points you can get in a round would be 12 points in all 3 weapons.
- You don't get points more than once for the Default weapon.
- Winners also get the points for being in the podium and top half (where applicable)
Buy and equip skins for each of your weapons.
You can see your levels and mastery points here.