Weightless is a "Minecraft, But" style challenge pack where Gravity decreases over time.
Starting from Day 2 the global gravity will decrease by 1% every in game hour (Roughly 50 real second), eventually dropping to 0% by Day 6. You may use this pack to challenge yourself in any way, whether it be to kill the Ender-Dragon or slay a Warden.
All items now have a Weight value from 1 to 3, increasing your personal weight the more items you hold, allowing you to keep some level of normalcy later in the challenge, however keeping high-weight gear on you will also slow you down and increase the amount of fall damage you will take! But there may be a special secret for those who wish to engage in item hoarding.
Make sure to keep an eye on the Advancements tab to check on the current global gravity!