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+This magic wall converts rocks into diamonds and vice versa. Note that
+a magic wall can only be activated for some limited time. It can also turn mega
+rocks into nitro packs, nitro packs into mega rocks. Even flying diamonds and
+rocks pass them to be converted into each other, but they do that from bottom to
+up, of course.
+
+The duration in seconds for which magic walls are active is configurable.
+A duration of zero will let the wall run forever.