How about a modification to the twin numbers feature? I call it 'mystery twin numbers'. This feature would be a feature award with an associated 'reverse time tree'. When awarded, the player would see that they have this feature, but not which numbers are the twin numbers. The twin numbers would be revealed based on the 'reverse time tree' -- the default is 'After 5th ball potted', but feature awards could improve it to 'After 5th ball shot', 'After 4th ball potted', 'After 4th ball shot', 'After 3rd ball potted'. The difference between 'potted' and 'shot' is when the ball lands in a numbered hole vs. pass through the gate.

I can imagine the relief when you have this feature lit with 'After 5th ball potted', pot the 5th ball, and see that you suddenly have a winner because of the twin numbers that were revealed. Or the disappointment that you landed next door to an angel.

I can imagine the skill needed if you have this feature lit with 'After Nth ball shot'; after the ball passes the gate onto the playfield, the player needs to look up, see which are the twin numbers, and then adjust strategy in real-time. A partner would be helpful here, calling out the numbers.

I can imagine the frustration of getting the feature lit with 'After 3rd ball potted', only to find that 2 of the 3 potted numbers are the twin numbers -- essentially losing the feature!

Only certain twin number pairs should be possible so as to eliminate, or at least make it very rare, that both appear in-line or the same scoring section. For example, if twin numbers were added to a magic screen game with a blue section, no two blue numbers should be paired.

Me too. Bally actually did something like this.
https://bingo.cdyn.com/machines/bally/crosswords/

I played this machine at Phil Hooper's home 15-20 years ago.

Here's a game that could run parallel to the main game, where the player must pot 1 of 5 random numbers, then 1 of 4, then 1 of 3, then 1 of 2, then 1 of 1.

Imagine that these 15 numbers are displayed in an inverted pyramid on the backglass (like bowling pins with an additional row), so the player can see and plan his path through the pyramid.

The pyramid of numbers could also be widened, perhaps. Maybe up to 10 additional numbers could be awarded and added to the pyramid, and they might appear at any level while still maintaining a pyramid shape. Meaning that as additional numbers were added to the pyramid, the pyramid would be constrained to 7/6/5/4/3 numbers for the top through bottom row. For example, say the player were awarded two additional numbers and they both happened to be awarded in the bottom row. At this point, the player would need to pot 1 of 5 numbers, 1 of 4, 1 of 3, 1 of 2, and then 1 of 3. If he went for additional numbers, any that are awarded could not also be added to the bottom row of the pyramid, as it is already "full".

The award should be substantial if the player manages to complete this game. It could be played as an all-or-nothing game where you have to complete the pyramid, or you could allow the user to stop and cash out after making the first three or four levels of the pyramid. (I like the all-or-nothing idea for this one.)

Create and build your own non-traditional 25-hole and 20-hole layouts? Now that opens up all kinds of possibilities!

There was at least one game, Touchdown, that tied a feature game award to red, not green, odds. Touchdown had a feature that, when lit, "4 star numbers awarded Red 5-in-line".

https://bingo.cdyn.com/machines/bally/touchdown/