Basicly a task that is completed by default but "uncomplete" once you do the action

Here is an exemple

You have a normal task that complete once you get a Diamond Axe
It's negative version would be that it is complete UNTIL you get a Diamond Axe, even getting rid of it WILL NOT complete it back

For Lockdown mode, allow to have an objective you need to try and not do or else the other will get the point

In normal mode tho, it is a bit useless

What use case do you have in mind for that?

Does it really require other teams to be involved? Let's think about this for a moment.

To me, it could be as simple as "do not pick up item X", "do not visit biome Y", "do not kill entity Z", etc. If someone failed and did what they were not allowed to do, that "don't do" kind of task would lock, and consequently, the entire team would not be able to fully complete the column/row.

This has the potential to make the game even more interesting by forcing players to achieve something in a way they would have never done if they were not forced to.