Getting river letters.
Use Whirlpool Challenge. shoot the plunged or kicked out ball into the whirlpool. hold the right flipper up and steer the light to the inlane. shoot the first ball into no way out with a very early flip, and hold. flip the left flipper 3 times to move the light back. cradle the second ball, and shoot it into no way out as well. At this time the first ball will be back to the upper flipper, and provided you dropped your flipper in time, you can then shoot it into the whirlpool (EASY shot). The other ball will follow behind it, and can be shot in again before the first one kicks out of the lost mine. You now have both in the lost mine kickout at the same time again, and can repeat your letter steering stunt. You will be at river class six in no time.
This is doable in single ball play as well, but it's slower.
Use Whirlpool Challenge. shoot the plunged or kicked out ball into the whirlpool. hold the right flipper up and steer the light to the inlane. shoot the first ball into no way out with a very early flip, and hold. flip the left flipper 3 times to move the light back. cradle the second ball, and shoot it into no way out as well. At this time the first ball will be back to the upper flipper, and provided you dropped your flipper in time, you can then shoot it into the whirlpool (EASY shot). The other ball will follow behind it, and can be shot in again before the first one kicks out of the lost mine. You now have both in the lost mine kickout at the same time again, and can repeat your letter steering stunt. You will be at river class six in no time.
This is doable in single ball play as well, but it's slower.