buster blader the dragon destroyer swoardsman effect not working
Buster bladers effect states:  

Dragon type monsters in your opponents possession cannot activate their effects


Normally this would prevent Destiny hero - Plasma from activating it's absorb effect.
However, Plasma has a second effect:

Negate the effects of face-up monsters while your opponent controls them. 


This is a continous effect, so it doesn't activate and so isn't blocked by Buster blader. This means that Buster bladers effect is negated and so can't stop Plasma from absorbing him.

For completions sake, in the case we have two monsters (e.g. 2 Plasma, or jinzo vs skill drain) that would negate eachothers effect. the one first on the field will win out and negate the other one.