This might go too far, as these are Willy games anyway, but is there a downloadable editor, what allows this kind of things?
IF certain_condition = TRUE THEN make certain_tile(s) appear/disappear/change_colour/flash/change_to_another_tile_type
IF certain_condition = TRUE THEN make new_guardian appear : SET guardian_life_time = nn_seconds : SET guardian_movement = mm (normal horiz/vert, only once go normal horiz/vert then stay still or disappear, only one-way horiz/vert, only once go one-way horiz/vert then stay still or disappear, stay still, flash)
IF certain_condition = TRUE THEN make certain_guardian(s) disappear/stay_still/flash_and_stay_still/flash_and_stay_still_nn_seconds_then_disappear
Bad thing is if these options are over used, they can turn Willy game to "ordinary any other platform game". Good thing is if these options are used wisely and rarely, very interesting effects can be made to certain rooms. Strange actions in certain rooms aren´t exactly a new thing in Willy games, though, as Jet Set Willy has out-of-ordinary room already, Rescue Esmeralda. In Manic Miner Eugene goes mad when you collect the last object. Solar Power Generator is not ordinary room either.
Appearing and disappearing tiles, or tiles changing to other type of tiles can cause interesting situations to rooms, like making possible to pass to certain direction or collect all objects, by adding new tiles for jumping upwards or block Willy´s path with a wall or floor or change floors to fire tiles. Many things could be done with these options. But perhaps not suitable for 48K memory limits?
Does JSWED coder or any other editor coder read this forum regularly to see my question?