In previous minecraft snapshots, the mining fatigue status effect did not allow the player to hit entities if the level was high enough (for example mining fatigue 255 did not allow players to hit entities). I believe this was extremely useful and should not have been removed. No, what it can be used for is not a replacement for the scoreboard team based friendly fire. Hopefully removing it was just a mistake, and I hope it will be added back soon.
Comments 4
In previous snapshots you weren't even able to hit any entities while having mining fatigue 255, the highest level available for the status effects. When you had a high level of mining fatigue, it lowered the radius of how far players can hit other entities. NOT DAMAGE. Not being able to hit things prevented any sort of knockback. Similar to the friendly fire option you can use in teams, but for only specific players and for a certain amount of time.
When you had a high level of mining fatigue, it lowered the radius of how far players can hit other entities. NOT DAMAGE
That is incorrect. It's a myth that Mining Fatigue affects anything combat-related pre-1.9, and in 1.9 all it affects related to combat is attack speed, not range or damage. You were thinking of Weakness, which prevents attacking when your damage dealt is 0. Please take a look at the wiki: http://minecraft.gamepedia.com/Effect#List_of_effects
Extremely high effect levels are unsupported.
Are you sure you're not looking for Weakness, which does exactly as you're describing? Mining Fatigue does not affect damage dealt.