Leaving aside how template stacking makes it unclear what the actual race/base creature should be--being half-illithid gives a creature four tentacles; being half-farspawn gives it up to four more, and being a voidmind creature grants one more psionic tentacle. Each template specifically says that it gets these in addition to its other natural weapons, though the voidmind template says that a creature uses its psionic tentacle "if the base creature doesn't have natural weapons".

The creature becomes amorphous and extrudes its psionic tentacle, then makes a full attack using its tentacles. How many can hit in a round, and what are their attack penalties?