Okay.I will do one.
START
1-Create the level and save it.I will create not so fancy level,just to show.
2-Create a new layer and 3 new events.(If you don't know how,click "View" then "Layer" or "Event" on editor tabs.
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- I'll call them the layer "Mushroom" and the events "Mushroom Stop","Mushroom Move" and "Mushroom Again",but you can name them whatever you want.

The circled on red is the events and layers I created,the one in green is where you will find "layers" and "Events"
3-On the Event "Level Start"(He is aerody on events,no need to create other,if you are aerody using "Level Start" event for another thing,make another,go to "Auto Start tab and check "auto start when game start) Go To tab movemets,then on "Vertical Speed" put the speed.A positive number go down and a negative one go up.Put the number with the speed you want it to move,then select the layer you created and click "Add".On first of the events you created,put the layer.With the speed "0" and click "Add".On the other,the second one,put the same speed as the "Level Start" but contrary(If it was positive(Down) put this one negative,if it was negative(Up),put this one positive.Then select the Layer and click "Add" and on the last event you created,put the speed "0" again,put the layer and click "Add.".Also,if you want them to move up,put hem on "Vertical Speed",not "Horizontal",i'm making one that moves left and right.It's just put on "Vertical Speed" to make them move up and down.
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- Here's what you do:

On Green,the current event.On orange,the "Add",and atop it the event selection.On Blue,the speed,on yellow,movement.(Don't forget to do same thing with the other events as well)
4-Now trigger the events.On level Start event:Click on "others" tab,and Select the next event.On "Level Start",the mushroom will go down,and will trigger the "Mushroom Stop".Even if you don't want the mushroom to stop moving,you MUST do it.Make the mushroom Stop trigger Mushroom Move,that will make them go up.Mushroom Move must trigger mushroom repeater,that will trigger "Level start" to everything start again.Then,select the delay.The "Level Start" will start when game start as a default(duh),so don't need to worry.As for the delay,for example,when Level start starts,how many seconds you have to wait for it to go to the another direction? that's it,for example,if you want the mushroom to go up for 1.4 seconds,set it as 1.4 seconds,on "Mushroom Stop" and "Mushroom Repeater" if you want them to stop,set them as any value of seconds,if not,set them as default "Instant".On "Mushroom Move",set same time you placed on "Level Start",in my case,1.4.
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On green,current event "Level Start".On yellow,the "others" tab.On blue,the delay.On red,the event it will trigger after the delay of time has passed.Also,do with the other event,remembering that every event will trigger the next one,and the last will trigger the first one to repeate the process on a cycle.
5-Now the events part is over!Pick up the Mushroom on the blocks tab of editor,sizable and SMW,be sure that their layer will be "Mushroom",any thing that you put as "Mushroom" layer will now move that way.Also don't forget to adjust that block size with the pad.
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On Blue,the pad to incresse the size of the mushroom.On Green,where are the Mushroom is(I'm sure you aerody knew that,but i'll add it anyway.)And on pink,the layer showing that the mushroom is inside it.If the name of the layer isn't on that place,then select it and place.
6-make sure the layer "Mushroom" is checked on "Layers" tab,if not they won't will appear on level until a event makes them appear.
7-enjoy!