if it requires the one above or next, I think a lock on it, or
a description, "this is locked, required x, y".
one that is easiest, but if next node is visible, the one require has a lock,
that need the one above or next (if it's visible) or always that has lock
left and right, the middle has a lock, or up and down, center is locked, if that has
a require tag on it.
this is what I have, require x, y always are visible with a lock icon,
otherwise visible when one of the 2 is visible and a lock by then.
lock = require 2 nodes or more, depending on the &&, so max is 4 on all sides,
which can be used for the most special ones or best ones.
if you make the lock visible as always (regardess if it false), you can see
that it require 2 or more nodes, the rest of the nodes can be invisible,
because you cannot see the path towards to it.
see what is easier for you to impliment it.
description personally "this node is locked".
the reason for that is for them to figure out how to unlock it as a player