Period 4-1[edit]
The first half of this period contains a considerable amount of water. Fortunately, you can find not one, but two Waterproof items along the left side of the stage, along with stairs to an underground tunnel. Another stairwell can be found just across the stream, which you can cross without fear as long as the opposite side is clear. Behind the waterfall at (1), you will find a treasure room where you can collect points and an Award Medal. You can save a precious Waterproof by simply activating a Super Charger and run into this treasure room, but you may also do this after visiting (2) below to technically use a free Super Charger.
Your next goal should be to stand in front of the block at location (2). Bomb this block three times, and it will disappear. If you walk into the water, and head right, you will discover a pool just like the one in the first period that kills all of the enemies on the screen, and doubles the number of most of your inventory items! Don't miss it.
From here, you can extend a little further to the right before you appear to encounter a dead-end. The fact is that a number of blocks on this stage can be blown up with bombs. They are indicated by the red circles on the map. Choose whichever block you wish you destroy and bomb it until it is out of your way. At this point, you will have no choice but to use a Waterproof item in order to continue. If you choose, you can visit the steps in the middle of the water, and explore the underground tunnel for items and points, but you will have to use another Waterproof item when you climb back up the steps, or you will drown in the water. A waterfall will prevent you from staying in the water, so after you explore the land region below the water, you will need to use up another Waterproof item in order to survive the walk across the last section of water, and bomb one of the two blocks that bar your access to the remainder of the stage.
The remainder of the stage takes place on land. There is a stairwell hidden in the first large group of blocks. Beyond that, you will have to choose between the large middle pathway, or the two smaller paths on either side. When you get beyond them, the wall at location (3) can be bombed to discover a second treasure room in this period. Three out of the eight statues will cause items to stop appearing. Of the five that do provide items, you can obtain a Super Charger, a Lamp, a Powerball, a Time Stopper, and a Candle.
Finally, as you bomb the blocks in the very final portion of this stage, you will discover the Key near the middle of the screen, and a staircase just above it. It may not appear obvious how to proceed to the far right side of the room to reach the exit, but three blocks can be bombed and removed to grant you access to the exit, one of which is directly across from the Key.
Period 4-2[edit]
Hopefully you collected the Lamp from the second treasure room of the previous stage, or you have purchased extra Lamps from the Item Shop, because, like Period 2-2, this stage is completely cloaked in darkness. Use the Lamp to brighten the scene. Not only is this stage encased in darkness; it is also a looping stage where you must find the Chalice. There is a Waterproof item hidden in one of the blocks along the left side. There is also a block along the top wall at (1) that can be bombed to discover a treasure room on the other side. Here you will find a Megaton Bomb and Candle.
You'll need to use the Waterproof item when you are ready to cross the one and only stream in this period. Once you're beyond this section, you will enter the looping portion of this stage. This section is long, and doesn't contain many interesting features. There are four hidden staircases which would be good to visit if you happen to be running low on bombs. You'll have to travel all the way towards the end of the loop before you come upon something of interest.
After the upper wall pushes down into the stage, the lower wall begins to ascend. Along the top wall, you may notice one block set apart from the rest at (2). If you bomb it, you will gain access to a second treasure room. Of the seven statues in here, only two of them contain items. Bombing any of the rest will immediately cause the items to disappear. Here you can collect the two rarest items, a Megaton Bomb and a Lamp.
Beyond this treasure room, the wall along the bottom stops rising and settles back down. You must walk around and under the ledge to locate the Chalice which will prevent the level from looping around. Unfortunately, in order to collect this Chalice, you will have had to wander so far into the stage, that it will automatically begin looping around again before you can collect the Chalice. This means you will be forced to repeat the loop a second time anyway. If you attempt to visit the treasure room at (2) again, you will find no items.
Once you make it through the loop a second time, you will reach the end of the stage. It contains three paths, all of which are connected on the left. The bottom and middle paths are connected on the right. The right side of the bottom path contains a key, while the middle path hides one more staircase. Once you have the key, head up to the top path and access the exit.
Period 4-3[edit]
You may be surprised to discover that Period 4 contains a third stage, but you may be even more surprised when you realize that it is only one screen wide. If you have more than one Megaton Bomb in reserve you may be inclined to use it here to wipe away all of the blocks and expose the items and stairs beneath. However, it's worth hanging on to them and patiently bombing your way through the room if you don't mind taking a little longer.
There are two staircases to underground tunnels, where you can collect more items and points to boost the power of your ZED. The key is found along the left side of the stage. The only other feature of interest is along the top of the stage. The block marked at location (1) can be bombed to discover a treasure room. However, in order to access that block, you must bomb the block below it three times in order to clear it out of the way. In the treasure room, you can obtain one random item by collecting the Hudson Honey Bee tile from the bottom statue.
Once you're ready to exit the room, bomb the two blocks along the bottom of the upper path until they disappear, and proceed to the goal.