As far as improving flicker...no. Sprite0 would still be split among the 4 monsters (the existing energizers are all missile0 and do not affect the flicker of sprite0).
However, making the energizers use playfield GFX instead would increase the amount of cycle time that I could "reclaim" within the kernal...since no time would be wasted in handling the missile0 object (Note: playfield GFX is also used in Hack'Em...the energizer if still uneaten is ORA'ed into the dot data). An interesting wrinkle here would be to use Missile0 as the bonus "vitamin" instead of missile1 - with missile 1 free it could be used as a backdrop for the monster's eyes (it would be yellow, but it's better than nothing).
Just added flashing monsters...which was done by adding this:
LDA $80 ;3 bugfix for flash
AND #$08 ;2
BNE LF93D ;2
...just above this:
INY ;2 change to white pointer
LF93D: STY $F2 ;3 set monster color pointer
Working on trying to get rid of that annoying "bong" sound when munching
A siren is also in the works.