[Crow]

You can also counter this problem differently. If you have a wide range of tiles (you said you ran out of blocking tiles, so I guess you do) you could just lay the needed tiles over some already existing blocking tiles using addtiledef2(). For example, if you have some special mountain tiles, but there are no mountains near those watery cliffs, just use addtiledef2() in the levels where those watery cliffs are.