A feature that, when activated, stops any further stacking opportunities by deactivating other targets.
The Ringmaster in Cirqus Voltaire: When stacking in Cirqus Voltaire, The Ringmaster Multiball must be the last feature you collect. Starting the Ringmaster Multiball deactivates any progress toward the Juggler, Strike an Arc, or Highwire Multiballs.
EXCEPTION: When Ringmaster Multiball ends, there is a grace period of less than 3 seconds. During that time, if you start one of the other Multiballs, Ringmaster Multiball will also restart.
Iron Monger Multiball in Iron Man: Starting Iron Monger Multiball deactivates any progress towards BOGEY, War Machine and Whiplash Multiballs.
Whiplash Multball in Iron Man: Starting Whiplash Multiball deactivates any progress towards BOGEY, War Machine and Iron Monger Multiballs.
However, this does mean that you can stack BOGEY + War Machine + Iron Monger Multiball or BOGEY + War Machine + Whiplash Multiball. Whichever stack you choose to go for, War Machine Multiball must be started before trying to start Iron Monger Multiball or Whiplash Multiball.