This plugin adds extra challenge to the game, whether you want players to struggle climbing mountains or suffer on a moon-like planet with pockets of air deep underground, it's up to you with Thin Atmosphere. Even if you just want to discourage players from being too high up, it'll work for that too.
When a player goes above the start-altitude value, they begin to lose air bubbles as if they were drowning. The higher up they go, the faster the air bubbles are lost until they reach the end-altitude value, at which point they should be dead.
ticks-per-decrease - Air bubbles decrease every x amount of ticks, 5 seems rather stable in my testing
start-altitude - The altitude where players start to lose air at
end-altitude - What altitude the player loses all air at (unless multiply-diff enabled)
multiply-diff - Multiplies altitude difference by 4, makes air loss more gradual
offset - Helps prevent oxygen bubbles from flickering, increase until flickering stops, may need to decrease if multiply-diff is off
