The Ceremonial Dagger is a Yautja weapon, used by warriors as a last-resort weapon or a weapon to take trophies from fallen enemies. It is first seen in Alien vs. Predator when the Predator, Celtic, attempts to finish off Grid before the Xenomorph can escape from his Net. However, Grid bursts free and head-bites Celtic. It is seen again later when Scar cuts a dead Xenomorph apart to fashion weapons for Alexa.
The Ceremonial Dagger is a relatively new discovery, associated with the blooding rites of young Predators. Its primary use is to remove the protective layer of skin of a Xenomorph but could also be used as a close-contact weapon if need be. The blade itself is made of either the bones or the 'resin' of a Xenomorph, making it resistant to their acidic blood.
First featured in the Alien vs. Predator film, the ceremonial dagger attached to the right shins of all three starring Predators. It is treated to resist xenomorph blood. It looks like the trophy which is obtained with this weapon has more value in the Predators' world than other ways of killing a prey, since Celtic let himself open to Grid's attack, just to finish him off in a ritual kill.
Celtic was the first Predator to use the Dagger, but died before he could kill an alien with it. But, Scar used it to make weapons for Alexa in AVP.
After Wolf gets the distress signal he gets his weapons and after he picks up his backpack the Ceremonial Dagger can be seen.