Got a mod pack that makes survival extremely tough? Say Chaos Core for example? Well with Adaptive Tick, your game will slow down as you lose health and pick up speed as you regain health. Say you're at 5 hearts; the game will be running 50% slower. This works by setting the rate of the tick to your health.
If multiple players are active, it tick-syncs the health of the player who has the least amount of health.
Since the /tick command is a permission-level 3 command, this must be installed on the server. And you must change the function-permission-level=2 to function-permission-level=3 in server.properties.
Sadly, and as of Minecraft 1.21.11 you can't adjust the permission level of functions in singleplayer worlds.
Fortunately, this can be mitigated and bypassed with mods that adjust /tick's permission level. See TickLowerPerm for singleplayer options.
See my other mods