My fellow, tenuki has just chipped in an idea: neutral discs could dissappear when they create a line of 4, making all discs above them fall down.
Another idea:
How about rhombus-shaped 10x10 board. Discs fall down diagonally (from either left or right side) and can block making part of the board unplayable and stick to other discs.
(gem) Hvis du vil spare båndbrede kan du reducere mængden af information der vises på dine sider under indstillinger. Prøv at ændre antallet af spil på hovedsiden og antallet af beskeder per side. (pauloaguia) (vis alle tips)