The game's now at 26.5 KB. I think a good sized level 5 will be possible. Maybe 10-15 rooms. I will probably make 1 more enemy and replace the cannon graphics for this one. I only put 2 cannons in the fourth level, since I abused them in level 2 and 3.
I succeeded getting the hunting down the 4 enemies to unlock the gates event. 4th level boss took up 10 sprite slots, so that replaced bird object, cannon ball, and cannon graphics, and the time heart graphics. I placed the time and heart power up in the gate room. I did not want to add another variable to keep track of the time power up. I added an event that when you pick up this power up, then it'll close the gate in that specific room, forcing you to the boss room.
Now the fifth boss need to be drawn and programmed first. 1 more power up to be added since there's 2 unused object slots, so I'll use 1 of that for the power up, maybe one more towards the boss.