Poor Bushroot whatever happened to him is not good. He tried to merge animal and plant DNA resulting in him turning into a zombie/plant/duck monster. I think that maybe the zombie part was not as immediate as the other changes that Reginald Bushroot went through. My thoughts are that he slowly became a zombie after what happened in Twin Beaks. In the episode of the original Darkwing Duck series "Twin Beaks", Bushroot looked kind of similar to how reboot Bushroot looks. The town's strange properties could have triggered zombification.