If you want to unlock the following stage, just collect what is recommended in the list below:
Collect 2 Fantastic Four icons to unlock the Survival Killing Stage 2: Barge arena.
Collect 4 Fantastic Four icons to unlock the Survival Killing Stage 3: Underground arena.
Collect 7 Fantastic Four icons to unlock the Survival Killing Stage 4: Tikal arena.
Collect 20 Fantastic Four icons to unlock the Survival Killing Stage 5: Horus arena.
Collect 25 Fantastic Four icons to unlock the Survival Killing Stage 6: Elevator arena.
Collect 28 Fantastic Four icons to unlock the Survival Killing Stage 7: Shield arena.
Collect 31 Fantastic Four icons to unlock the Guard Granny stage arena.