There are some things you could add:
Level 1: You start the level without sword. Falling entry.
When you crouch the first time, a music is played. Normally, this crouch is after landing from the falling entry.
The crouch after a two-storey drop doesn't count. (I remember there was a mod that started with a two-storey drop.)
Room 5, tile 3 is pressed at start. On the original level 1, this closes the door behind the prince.
If this tile is a loose floor, it will drop. If it's a door or exit door, it will open. If it's a chomper, it will chomp once. If it's a spike, it will come out, then go back. (see also level 13)
Level 3: The closing sounds of the gate in room 2 can be always heard, not just in the room it is in.
"Approaching the skeleton" means touching tile 4 in any row.
After the skeleton falls off room 1, it will appear in room 3, middle row, tile 5, facing right, but only if room 3 is below room 1.
Checkpoint: Leaving room 7 to the left seems to be enough.
Level 4: There is a different music after going up on the level door.
Actually, the mirror is placed at the moment the level door is fully opened, but it is drawn only when the room is reentered, or if you go to that tile without leaving the room. (Which is possible only on an edited level.)
Also, after reentering, a music is played.
Level 6: If you fall out the bottom of room 1, you'll arrive to the next level. (Even if there is no room below room 1.)
A music is played when entering the shadow's room.
The jump doesn't have to be in the middle row, or to tile 3. If the prince enters a certain frame in the run-jump sequence (the frame where one of his feet touch the floor), and he is in tiles 1-5, the shadow will step forward.
Interestingly, if you put a potion or sword in front of the shadow, it will crouch instead of step, as if he was trying to pick it up.
Level 7: Falling entry. Works only if the player starts in room 17, bottom row.
If the player starts in room 17, but not the bottom row, an integer overflow will occur.
(Just like
viewtopic.php?p=11204#p11204)
Level 12: Sword disappearance: leaving room 18 to right seems to be enough.
Level 13: Running entry.
Flash when Jaffar dies.
After Jaffar died, entering any room from the right will trigger the top left tile of room 24. On the original level, this opens the exit door.
Interestingly, if the tile is not a button, but its modifier refers to a door event that triggers a level door, then the level door will open. (see also level 1)
If you put doors where the falling loose floors are, they are instantly opened, when you enter the rooms below.
Loose floors don't shake if you jump up, only when they will fall down.
Level 15: Letters appear. One of the potions is changed into an open potion.
A hurt potion takes half of your hitpoints instead of one.