Dig dug is easy enough to get through. The first 11 levels are unique.
Just pump all the enemies 1 at a time, and don't let them gang up on you.
From level 12-15, they repeat forever. There are patterns that will work up
to 15, and then after that, modify them for slightly faster enemies for the
rest of the game. The score goes to 9,999,990, and I usually quit at 1,000,000.
Here are my patterns from 13 onward, past level 19:
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