How to send a custom message to acquired actor without going through world variables?

No, the Bactor is not a sure actor, many actors can be Bactor, it should be acquired, not be get with a class or something

for example, a unit killed an enemy and get XP, we need to know whats the type of unit be killed to give 【XP of this type unit be killed】 to the killer

In this process, Bactor is not a sure unit, I need a way to send information and variable in this case, and for optimization reasons, it’s better not to create additional global variables, which consume too much computational power to find and read/write them over and over again