I can see some elements.
Hit into the tunnel to the institute, for a ball lock.
Upside down mode where the left flipper button activates the right flipper(s) and vice versa. or the under-playfield mini game, as someone said above.
Cycling to escape the vans video mode.
Spell out messages on a ouija board to unlock challenges.
Follow the lights (hit the current lit target) to find Will Byers.