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Smash up an elite sentry.
Destroy the cat's mobile fortress.
Complete all bonus levels.
Get a score of 1,000,000 in any level except survival.
Die with over 666 enemy bullets on screen.
Play 10 levels as Natalie.
Get A ranks in 20 or more levels.
Defeat the final boss and complete the standard set of 20 levels.
Beat the first 20 levels without upgrading your health.