Tyrant weapons and their effects. Need help to understand how it works.

Well, the first part buff is very clear:

[Tyrannical Charge buff]

- 1% more damage, healing and damage resistance for every 5 seconds in combat (Max of 10%).


Now the second part buff is weird to understand:

- These increases are doubled if affected by a Trophy Hunter buff.


Now, the questions:

What is this buff ? How I know that buff is active ?

- Is the Vision of Dendar buff from Empowered Chain of Scales ?
- Is a buff that's activated only if you wear any Omu hunt item (Fured Kiuno for example) ?
- The player must wear the Hunter's Keffiyeh helm from King of Spines hunt, to activate that buff ?

And:

- If the increases are doubled by a Trophy Hunter buff, that means we need only half of time to hit that 10% max increase (5 Tyrannical Charge stacks = 10% more damage, healing and damage resistance) ?
- Or means that, after 50 seconds in combat (10 stacks), we get 20% more damage, healing and damage resistance ?

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I've searched about this question earlier, but all the answers was unsure and not fully tested.


Thank you in advance.