Based on the moment consistency principle, the bubble threshold was determined by using the traversing method. A novel approach was proposed to identify bubbles and agglomerates from transient signals registered in a cold mode fluidized bed dealing with different particles. Bubble and agglomerate hydrodynamics including volume fraction, solid holdup, immigration velocity, and frequency were investigated. Adding fine powder promotes the formation of particle agglomerates at low superficial gas velocity and leads to a great bubble volume fraction at high superficial gas velocity. Bubble frequency increases significantly during the flow pattern transition from bubbling to turbulence bed. Compared with FCC particles, the mixed particles have a narrow bubble chord length distribution. The net velocity of agglomerates is positive in the center and close to zero or even negative in the vicinity of the wall. The agglomerate frequency in the mixed particle bed is significantly lower than that in the FCC particle bed.