How did I coded Bubble Girl in MMF? if you check my history and some of my newer bubble girl games, I could explain you in a simple way how to make the first step in platforming and make a game which is more decent:

What you need:
1 Hero (Even two if you want, in a 2 player game)
Several monsters
Platform
Weapon
Power ups.
Stage exit
Power Bar indication

In this case, you got yourself Bubble Girl and the Goomba looking characters, you got yourself a bubble to shoot and you got yourself power-ups.

First, place the objects on the screen, Place the hero, and the monsters and several platforms. This is simple

Now, Into animating I mean, making the monsters move:
This is a special thing that not many new users know:
For a Goomba type of enemy you have to define a Platform movement! Yes! This that meant for players to be used! Now set it to player 2 because you are player 1, and in the event editor set this condition: At start of frame: Disable movement of player 2. This way, characters with the platform movement of player 2 won't move when you press any button, but! They will move by a programmed movement!

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Program the Goomba:
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When colliding Obstacle: Stop
Set Value A of Goomba to Random (5) every 1 second (Or it can be every 0:70Milisecond or any value you desire and see that work!)
When Goomba's Value A is 1: Set direction to Left + Start movement + set speed to X (25 to 45 is recommended)
Same with:
When Goomba's Value A is 2: Set direction to Right + Start movement + set speed to X (25 to 45 is recommended)
If you want it to decide and move faster from time to time, Then set the random value A to (5), and repeat these two steps above only with higher value: For example:
When Goomba's Value A is 3: Set direction to Left + Start movement + set speed to X (45 to 65 will be recommended this time)
When Goomba's Value A is 4: Set direction to Right + Start movement + set speed to X (45 to 65 as well!)

Now the enemy is starting to move! When value A will be 0 it will automatically stop! Be sure about that and no worry! Hope you understood!

Now, Value B will be set for hit points:
Each time Active Object(Weapon, Bubble, Etc) will collide Goomba, add 1 to value B. (Or even 1+random number if weapon is stronger!) + Flash Goomba for 4 Miliseconds + Set Flag 2 on
It will be always good if every single Goomba will have a different hit points from each other: Do it by setting this event: When flag 1 of Goomba is off: Set flag 1 on + subtract random 3 (or more) from Value B. This case it will add 0 to 2 more hit points a goomba!

Every 60 Miliseconds, if Goomba Flag 2 is on: Set off Flag 2 of Goomba + Reappear Goomba

Now, Killing a goomba:
When Value B is more than 3 (Or any value you choose) destroy Goomba + Create Stunned Goomba at 0,0 of hot spot of Goomba
Stunned Goomba is actually a new object of a Goomba! Draw a Goomba in stunned mode, then make sure it will be created when a regular Goomba Object reach it maximal hit-points!

For stunned Goomba:
Like in Bubble Bubble, stunned Goomba will recover after several seconds so:
For Stunned Goomba: Every 1Milisecond add 1 to value A.
When value A = 400 + run this event only once when loop -> flash object
When Value A = 500, Destroy Stunned Goomba, And create a regular Goomba at 0,0 of hot-spot of Stunned Goomba

Remember! Stunned Goomba has gravity as well as a regular Goomba! Set it's movement to Player 2 platform. It will be disabled for player's movement as you already set that condition earlier!


When Stunned Goomba collides background: Stop

To kill the stunned Goomba:
When Bubble Girl (Or hero) collides Goomba -> Destroy Goomba + Create Dead Goomba.

The Dead Goomba is another object which is part of the whole enemy! It will often leave a power up behind him:

To leave a power up:
When flag 1 of Dead Goomba is off: Set Flag 1 of Goomba on + set value A of Dead Goomba to random (24 will be decent! It will have a chance of 1 to 24 to give you a power-up!).

When Value of Dead Goomba is 1 (Not 0! As it will always leave you a powerup if you choose it's default value! Remember! It must be changed with a random number!) Create power-up (Usually heart) in 0,0 hot spot Of Dead Goomba

Cleaning the Goomba out of screen:
When Goomba leaves the play area on bottom: Destroy
Remember! Dead Goombas or monsters has gravity of Player 2 platform movement as well!

Now: Special effect for Stunned and dead goomba:
If Value B of Stunned/Dead Goomba is less than 30, Set Y position of Stunned/Dead Goomba to Stunned/Dead Goomba - 2.
Paste this event several times but this time change it to: If Value B of Stunned Goomba is less than 25, 20, 15, 10

You can even paste the same condition as above several times with the same value! MMF will treat both events, so don't worry about it!

We got ourself our first enemy! All others will be working the same!

Spitting Goomba:
Spitting Goomba is same like Regular Goomba, only it has a weapon:
Every 1 Second Set Value C of Spitting Goomba to random 24.
When Value C of spitting Goomba is 1(Or 2 or what you desire) + run this event in loop only once + when value A of Spitting Goomba is 1-> launch spit from Spitting Goomba to left direction

When Value C of spitting Goomba is 1(Or any given number again) + run this event in loop only once + when value A of Spitting Goomba is 2-> launch spit from Spitting Goomba to right direction

Otherwise: The same but: Create Spit.
Now if Value A of Spitting Goomba is 1, then set Value A of Spit to 1
If it is 2, Then Value A of spit will be 2!

Make spit a player 2 platform movement
When it leaves the play area on bottom: Destroy Spit

If Value A of Spit = 1 -> Set speed of Spit to 64, Set direction to left. Start movement.

If Value A of Spit = 2 -> Set speed of Spit to 64, Set direction to right. Start movement.

There you go! A shooting or spitting Goomba!

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Programming Bubble Girl (Hero):
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Default player 1 platform movement will do it for us this time. It will also be manipulated later!

Set collision that stop the Hero as you did with everything else:
When Hero colliding background -> Stop

Now, When pressing Left button, Set value A of Hero to 0
When Press Right Button, Set value A of Hero to 1

When pressing Fire Button 2 + Value A equal 0 + Value B equal 0(Why value B? It will leave us to have a different weapon on a different value of it!)
Shoot Bubble (Weapon) from Hero to left direction, Set animation to shoot

When pressing Fire Button 2 + Value A equal 1 + Value B equal 0
Shoot Bubble (Weapon) from Hero to right direction Set animation to shoot

But make sure! Don't use the standard shooting animation! Create a new of your own! A custom animation and name it Shoot of you want, this way, when you have a 3 direction way weapon, it will make sure it will shoot all projectiles!

When animation Shoot is over: Restore animation sequence

Making Bubble Girl get hit:
When Hero overlaps with Goomba, Value C equal 0: Set Value C of Hero to 3 -> flash Hero for 4Miliseconds + Add 1 to Value A of Power Bar, Set animation of Power Bar to Power Down animation
Every 1 when Value C of hero is greater than 0, subtract 1 from Value C of Hero
When Value C of Hero equal 1, Make Hero reappear

Kill Bubble Girl:
When power bar's Value A worth 5, Destroy Hero, Create: Dead Hero
Now, as you already seen with the monsters: You can set everything you did to dead Goomba to Dead Hero (Everything but item leaving since it is just silly to have in this case! Or maybe not?)

When Dead Hero leaves play area on the ground, restart level, or... To be more complecated: Jump to number of level: Global Value A!
This is a trick! So when you use it, make sure that on start of frame, Set Global Value A to Frame's Number

Heart Power Up: When Hero Collides Heart + PowerBar Value A worth more than 0, Destroy Heart + Subtract 1 from Value A of Power Bar. Set Power Bar animation to Power Up

Spread Shot power up: When Hero Collides Spread Shot power up: Set value B of Hero to 1.

Now remember the condition you had before? Make these lines of conditions:

When pressing Fire Button 2 + Value A equal 0 + Value B equal 0(Why value B? It will leave us to have a different weapon on a different value of it!)
Shoot Bubble (Weapon) from Hero to left direction,
Shoot Bubble (Weapon) from Hero to left and up diagonal direction,(Choose one of the diagonal directions)
Shoot Bubble (Weapon) from Hero to left and down diagonal direction,(Choose one of the diagonal directions)
Set animation to shoot

When pressing Fire Button 2 + Value A equal 1 + Value B equal 0
Shoot Bubble (Weapon) from Hero to right direction
Shoot Bubble (Weapon) from Hero to right and up diagonal direction (Again, choose the desired diagonal direction)
Shoot Bubble (Weapon) from Hero to right and down diagonal direction (Again, choose same here!)
Set animation to shoot

This was the spreadshot powerup:

Create invincibility:
When Hero collide with diamond: Play invincibility music, Destroy diamond, Set Value C to 32
If Hero collides with Goomba and value C is more than 5, destroy Goomba, Create Dead Goomba At 0,0 of Goomba

When Value C of Hero is 5 stop invincibility music, flash Hero for every 4Miliseonds

Remember you already defind Value C as a recovery timer! So don't worry! It will count down as you already set it! This way, Enemies won't kill you instantly hit after hit, but you will have a gap of recover and escape!

Stage Exit: It will open when all enemies has been killed!
If you know how to group, set Goomba at a group qualifier, such as Enemies or any other Group: Group X, Y, Etc'. Set this too all other monsters that you have!

When Group(Enemy) number at zone: X0 to X640 and Y0 To Y480 = 0, set Exit door to open animation, Set flag 1 of Exit Door to on

When Hero collides Exit door and exit door Flag 1 is on, go to next frame!

Now! You got the basic setup for any Bubble Girl or Taito's style Bubble Bubble sort of game! This concept will be on every level with your later definitions as springs, more monsters, bombs, spikes, etc...

A typical game in this style have 30 to 60 levels often, 10 to 15 types of enemies and several bosses! Do your best to make a better game with the tips I gave you! Enjoy!