Seneschal Bestiary Knowledge [SPOILER]

Minimum requirement to get 3*, you must at least finish the whole game 3 times.
Proceed a very long battle so Patience since the dialog trigger is random.

The battle happen during my 3rd New game plus. All I did is initiate a long battle until pawn trigger dialog such "I've learnt the beast" 2-3 times. The last dialog happen when Seneschal defeated

Timestamp dialog trigger:
2:57
9:09
10:16