The mana buffer is only activated when incoming damage would exceed your current hit points. If this new mechanic didn't exist, you would simply die. So, it's not useless at all.
How it works:
- The overkill amount is multiplied by 8 and subtracted from mana.
- Additionaly, 25% of the character's maximum mana is consumed, but this additional mana consumption can only trigger once every 2 seconds.
- If mana runs out, the character dies.
For the mechanic to be more effective, it's recommended that you keep your mana as full as possible. The lower your mana, the less durable the barrier will be.
It's worth noting that the mechanic was created to prevent deaths from unexpected combos. Therefore, it probably won't be very useful in dangerous traps or when you lose connection with the game.
When the barrier is activated, you should heal your health very quickly. The barrier should remain active for the shortest time possible. Otherwise, your mana will quickly deplete and your character will die.
Source: https://www.tibia.com/news/?subtopic=newsarchive&id=8833
