The left ramp, right ramp, and right lane give Cheese letters: the right ramp can be comboed. Spell Cheese to light the right ramp for a mystery award and a jackpot advance. Once the jackpot is high, finish the Mouse Trap standup targets and lock both balls for multiball. During multiball, hit both lock shots again to light jackpot on the right ramp.
On the plunge, one of the three top lanes will be flashing. The flashing lane cannot be moved with lane change. Making a skill shot into the flashing lane scores 100,000 points multiplied by the current ball number, as well as instantly advancing the jackpot value.
At any other time in the game, going through a top lane lights it, the lights can be moved with lane change, and lighting all 3 lanes advances the bonus multiplier to 2x or 3x. It's very rare for the ball to end up in these top lanes; when it does happen, it's almost always due to pop bumper luck, so don't rely on multiplying bonus as a strategy. End of ball bonus isn't worth a ton of points in the grand scheme of things anyway.
The 5 standup targets on the left spell Mouse, and the four on the right spell Trap. Each target scores 5,000 points. Completing both Mouse and Trap lights the locks on the left orbit and right lane. Letters in Mouse and Trap can also be spotted by lit in lanes.
Value of this shot starts at 50,000 points. Making the orbit scores the value and increases it by 50,000. When worth 200,000 points, this orbit also lights extra ball on both ramps. The catch to all these points is that the orbit must be comboed: shooting the left orbit feeds the ball to the right flipper, and if the orbit is not made again within 5 seconds, the shot value resets all the wya back to the base 50,000.
When locks are lit ("traps are set"), this left orbit is one of the lock shots. Shots made to the left orbit when lock is lit cannot count for the progressive big loop award.
Whenever the retractable targets are up, making 1-2-3 in order will lower them, revealing the center ramp. Making the center ramp scores 100,000 points and lights the left and right ramps for Million Advance. Also, completing the 1-2-3 targets or making the center ramp 3 times will relight the left out lane kickback if it was not already on.
The left ramp, right ramp, and right lane are almost always lit for Cheese. Each letter in Cheese scores an increasing value from 10,000 to 50,000 points. When Cheese is spelled, the Mouse Hole is open on the right ramp. Making the Mouse Hole awards the Cheezy Bonus, which is a mystery award that can give Special, Extra Ball, 1,000,000 points, or a random award between 100,000 and 500,000 in multiples of 50,000. Collecting a Cheezy Bonus also increases the value of the multiball jackpot, which starts at 1,000,000 points at the beginning of the game for each player; jackpot advances increase the jackpot by 500,000, up to a maximum of 4,000,000 points. Collecting a jackpot resets its value. Unlike some other games from this time, jackpot is not shared between players or across games.
Once 1-2-3 on the center targets has been completed in order and the center ramp has been shot once, the left and right ramps will both light for Million Letter. From here, either ramp awards a letter in Million. Make 7 ramp shots to spell Million and the Mouse Hole will open on the right ramp for a 1,000,000 point shot. This shot is not timed, and once the Million Letter lamps or the Million Shot are lit they will typically stay on until collected, even across balls.
The target at the end of the right lane shot spots a Cheese letter (see above). When locks are lit by spelling Mouse Trap, the right lock is in this lane. There is one other feature, though; if the right ramp is made twice in a row consecutively without any other switches being hit in between, this lane will light for Double Scoring for a few seconds. Shooting the target in the right lane while Double Scoring is lit starts 2x playfield scoring, which runs for 15 seconds. This is a good time to hit as many ramps and left orbits as you can.
Spelling Mouse Trap lights the locks at the left orbit and right lane. Making both locks starts multiball. There is no playfield multiplier during multiball; everything is in play for normal scoring, with the locks lit. When a ball is shot into either lock, it will stay there for a couple seconds and be kicked back out; doing this causes the Set Trap insert to go from flashing to solidly lit. Shooting both locks lights the right ramp Mouse Hole for Jackpot for 15 seconds. Collecting the jackpot causes its value to return to the base 1,000,000 points, but multiple jackpots can be collected in a single multiball (and the value can even be re-raised by ramp shots before hitting the locks again, too). Failing to collect the jackpot means both locks must be shot again for another chance. If the game returns to single ball play while the jackpot timer is running, it will continue to run until the jackpot is made, the time runs out, or the ball is drained.
Bonus is advanced by pretty much any shot in the game (ramps, loops, lanes, targets). I have not yet made a specific distribution of exactly what shots award how much bonus. Bonus is generally carried over from ball to ball, and seems to be in the 150,000-250,000 range at the end of a typical three ball game. It's not much in the grand scheme of things, but I do still recommend trying not to tilt on ball 3 because games on Mousin Around can frequently be decided by a quarter million points or less.
2x and 3x bonus can be achieved by completing the top lanes once or twice in a single ball. This is very difficult and rare, so don't rely on it as a strategy; if your ball was going on long enough to actually get the 3x bonus, it was probably long enough for you to pick up other more lucrative scoring, such as a couple Cheezy Bonuses or a Jackpot.
Mousin' Around has a conventional in/out lane setup with a center peg between the flippers. The left out lane has a kickback that is on at the start of each ball and an be relit by completing the center 1-2-3 targets in order, or making 3 shots to the exposed center ramp. Both out lanes can be lit for 250,000 points by making the left loop.
The in lanes will both be lit for Spot Mouse Trap Letter until a multiball has been played; for the second multiball and on, only one in lane will be lit at a time.
The kickback can be set to be on to start every ball, on at the start of the game with memory, off at the start of the game with memory, or off to start every ball.
The in lanes can both always be on, always have only one on, always be both off, or function as described above where both are on for the first multiball and only one is on for subsequent multiballs.
The Million Letter lights on the ramps can be on to start the game, or they can turn off after each individual Million letter, requiring another center ramp shot to relight.
Cheese letters are carried from ball to ball by default, but this can be turned off.
The end of ball bonus can be reset between balls instead of carrying over.
The Double Playfield timer and the Jackpot timer can both be set to any time from 0 to 30 seconds; both default to 15.
The timer on the left orbit's value resetting can be anywhere from 1 to 5 seconds. Also, the loop can start at 150,000 or 100,000 instead of 50,000; or, it can require two or three 50,000 shots before advancing to 100,000. In other words, the extra ball can be set to require 2, 3, 4 (default), 5, or 6 comboed left orbit shots.
The operator has control over how frequently the Cheezy Bonus gives extra balls and specials. Both can be disabled outright. I am not aware of any ability to set extra balls and specials to be worth points for competition/novelty play.