Vanguard
Fry until your ship is black instead of pink (it will either start
playing automatically, or on the map screen, where you won't be visible
because the background is black too). The number of lives will be
random, and not change accordingly to when you die, just sort of on its
own whim. Eventually, your ship will revert to pink, and you'll have
to use the other controller, but you'll still have unlimited lives.
If you fly long enough on the board where you have to kill all the
enemies on the screen, you will automatically veer into a wall and the
board will be finished. So you can play more or less forever. Its been
running on its own for several hours now and should be up to at least
500,000... When you get the little E-boxes, you can extend the duration
of the invincibility a long time, because every time you run into an
enemy while the music plays, it plays that bit of the music over again,
so if the enemies are spaced out right, it can last for a really long
time...
In the Stripe Zone, you can choose to go either right or left. If
you go right, then only the enemies which reside on that side will
show up, and the same goes for the left side. The trick: stay on
the right side until the Energy Pod appears. Then take the left
path. The Energy Pod will rhythmically switch between a forward E
and a backward E.
On Vanguard, toggle select and you can see what appears to be .531
(the one is underlined) or .53L (the L is backwards) in a vertical
column flash on the screen. Freeze framing it on a VCR reveals that
there are two variations: one a brief flash, the other a picture of
the first level with the number and an unusually colored background.