question about DoT

[Zaft]

Use it on a Striking Dummy to see.

What I DO know is, if you apply a Dot, THEN use a damage buff, it will not increase the tick. The damage buff need to be applied BEFORE the DoT.

Correct. This is called a snapshot. When you cast any spell, the game takes a snapshot of both your stats and the targets stats, and applies those stats to your spell.

So, here are two examples:

1) You have a 20% damage bonus. You cast your DoT. Even when your bonus wears off, the DoT will continue to have a 20% damage bonus until it wears off.
2) Your enemy has 75% damage reduction. You cast your DoT. Even when their damage reduction wears off, the DoT will continue to deal 75% less damage until it wears off.

This is why it's important to not clip (recast before the final tick of damage) your DoTs.