A Few Effects

Antigravity lowers gravity by 15% per level. Antigravity potions are brewed with shulker shells, and at level III a player can jump roughly 55% higher than normal, reaching about two blocks, while stacked levels allow jumps of around four blocks. The effect changes gravity itself instead of raising the jump boost value.

Vulnerability is the one harmful effect the mod introduces, acting as the reverse of resistance and lowering the player's armor by 20% for each level. Vulnerability potions are brewed by corrupting resistance potions, which are themselves brewed with golden apples. Reaching extends the block entity reach by one block per level, so a player with Reaching II can place blocks about five blocks away and hit enemies at a distance; it is brewed with scaffolding.

The mod is client and server, so the server and every player need it. Files are published for Forge only, for 1.20.1, and the license is All rights reserved, so the code is not open source. Potion effect icons are fully opaque rather than partly transparent. The mod also adds a new hostile mob that inflicts effects; the author notes say it is found in the soul sand valley.