Marking

Yautja can mark themself with the blood of their prey for mood bonus. Modded Creatures are supported, though they may sometimes give unexpected results.

Base Mechanic
The basis of it is the kill count stat of a Pawn. The mod watch for the kill count of Pawn to go up, when it does it will check for the last kill and check if the kill is a worthy one. The worthiness of a kill is solely based on the stat Combat Power of any given pawns in-game. This stat is entirely arbitrary and is not affected by skills or equipments. The value is set by the authors of RimWorld or any modder that create new races.

This system is very specific and will not award a kill if a pawn your Pawn was attacking bleed out instead of being outright killed by a gunshot or a melee attack. So you NEED the killing blow for it to count.

Unblooded Yautja
To Mark an Unblooded Yautja, they need to make a worthy kill, then right click on its corpse with the Yautja selected and click the Mark option.

Unblooded Non-Yautja
To Mark a non-Yautja you need to have a Yautjain your colony.

To Mark the Unblooded Non-Yautja, they need to make a worthy kill, then right click on the pawn with a colonist Yautja selected and click the Mark option, after being marked once they may mark themselves futher as a Yautja would.