This was answered by METAL SLUG original team and the team includes the following staff:
■ KAWAI, the team boss and development manager, but was not involved in actual development
■ MEEHER, Lead Designer
■ AKIO, Graphic Artist, basic design of characters and machines, animation, supervision
■ SUSUMU, Graphic Artist, work on overall scrolling and supervision
■ CANNON or MAX-D, Graphic Artist
■ TOMO, Graphic Artist
■ KUICHIN, Graphic Artist
■ ANDY, Programmer
■ SEEKER, Programmer
1. GENERAL QUESTIONS
1) What was your inspiration for the METAL SLUG series?
We remember the series started based on one concept, 'Player-friendly action game with one joystick and two buttons.' At that time, there were a lot of comical games in this genre. In order to differentiate METAL SLUG from them, and because we could create some cool machines and lots of action, we decided the series' main theme was war with lots of things to shoot.
However, it was still a video game and we didn't want it to be too brutal just because we pursued reality for the look of the game. Therefore, we built the whole game world based on the following description:
'Gameplay will be sometimes comical, but also challenging at important points and always cool to look at and play!'
2) Has fan reaction on the series led to design changes?
There would be no reason to improve other features if you cannot have fun with the basics such as moving, jumping, and shooting, so we focused our time adjusting game balance by researching players' reactions during income tests and location tests before launch.
Also, if we drew too much detail in our graphics, it sometimes made enemy objects and attacks hard to see. This is a problem, which quickly reduces fun and gameplay enjoyment, so sometimes we had to forget about reality and, for example, change the enemy's bullet to a color that was easier to see.
The top priority we have always had was to let players play the game without being stressed. However, we sometimes broke this rule and made the players feel stress on purpose. By doing so, you will have much more fun and satisfaction after you overcome the challenge and win!
3) Which METAL SLUG game is your favorite and why?
NEOGEO CD version of METAL SLUG 1 and 2. They are not too hard and you can play them repeatedly since they have a Combat School mode.
Also, METAL SLUG 3 was one title we enjoy since we had to fix a lot of programming challenges over and over again.
4) Which character and/or weapon is your favorite and why?
They are Sophia and Megu in Combat School mode.
We also really like the shotgun because the range is so short that you have to risk getting closer to enemies to take advantage of the huge destructive power.
Lastly, we like the Morden soldiers because their programming is very complicated, but at the same time they are easy to beat!
5) If Hollywood was going to make a METAL SLUG live-action movie, what actors would you choose?
Main characters have birthplaces, so we would prefer to have actors from those areas.
For example, an Asian actress may be suitable for Eri or perhaps it may be a good idea to choose a Japanese actress.
General Morden should be someone who can act like a villain but at the same time who is intelligent and loved by viewers, such as Sean Connery or Jack Nicholson.
Allen is half naked and muscular in the game, so how about Hugh Jackman who is sharp eyed and strong? If he plays Allen, everyone knows that he'll come out on top! Also, the audience will applaud if he comes back in a sequel since he went missing in the first episode.
Regarding the world in the movie, it would be good to maintain the world of METAL SLUG games, but it might also be a good idea if we made a war movie. On the screen where soldiers are fighting, like 'Saving Private Ryan', it would be very exciting to see a sudden METAL SLUG appearance.
6) Is there anything you can share about the upcoming METAL SLUG projects?
Metal Slug has started as a side-scrolling action game, but it would be nice if we can broaden the franchise in other genres.
It would also be good to widen the world by focusing on other characters living in the METAL SLUG universe or creating more about the background and motivation of main characters.
7) Do you think we'll ever see a METAL SLUG cartoon, similar to Fatal Fury and Samurai Shodown titles?
It could be possible if we receive lots of requests from you guys!
8) Why do you think METAL SLUG has enjoyed such widespread popularity and long-lasting appeal?
METAL SLUG is basically a simple platformer/action game and it's simple control scheme allows casual gamers to play it quickly and easily.
Also, the shooting factor, (you avoid enemies' attack and shoot back), is well received universally.
Additionally, it is a 2D dot animation and maybe players can feel the love and detail that the artists gave to the game when they created them.
For all these reasons, METAL SLUG has become popular.
9) Would you like to take home a little METAL SLUG toy tank?
Yes, if it is high quality.
10) Are we going to see more classic game characters and enemies, such as Clark and Ralf of the Ikari Warriors in METAL SLUG 6, in future METAL SLUG games?
Could be possible with enough fan support!
It would be fun to have Leona from Ikari Warriors or Mai Shiranui , the female Ninja-like agent who has been sent from Far East area of PF forces.
11) Who is the best METAL SLUG player in the office?
It is obvious that fans are much better than any of us.
Income tests/location tests are a place to see who is better between developers and fans. We have had some experience in that fans easily beat enemy characters that we thought would be hard to beat.
12) What is the strangest thing a fan has ever done that you have seen with the METAL SLUG series?
It was the time when a fan in a Galford costume (from the Samurai Shodown series) came to the arcade and started playing a METAL SLUG game. Also, there was a fan playing the game in Iori (from KOF series) costume.
13) What is the strangest thing that has ever happened in the office during the development of a METAL SLUG title?
METAL SLUG is a game that challenges hardware capabilities, so while we were debugging/testing the game, one arcade cabinet caught on fire and broke!
14) What was the inspiration of the METAL SLUG tank design?
Well we want to say 'It's an original idea and we didn't get any inspiration from anything!' but we came up with the design from various manga/comics. animation, movie and other places.
15) Will we ever see Trevor or Nadia in a METAL SLUG game again?
You might see them in upcoming sequels.
We could use them as important characters in derivative titles outside the franchise.
2. DESIGN QUESTIONS
1) Has there ever been the temptation to add more commands/buttons to the METAL SLUG games, for additional attacks, etc?
We wanted to avoid any complicated commands from the beginning of the series, so even when we set up additional attacks, we didn't add any buttons or commands and tried to limit the configurations to be one joystick and three buttons.
2) What's the most challenging aspect of coming up with new and exciting locations and enemies for the heroes to fight in, but remain true to the METAL SLUG world?
It was always our proposition that we had to create locations and characters that we never saw in previous titles. That was a very challenging aspect. Especially regarding locations/stages, changing the visuals was not only important but also adding some 'gimmicks' to the location.
We had a hard time coming up with ideas to meet those requirements.
3) What's the wildest idea that you have come up that had to be cut from one of the games?
It was a stage which had a Dino Slug with a huge battery on the head of a T-Rex. The size of the slug was almost half the screen, moved forward smashing towns and had hand-to-hand combat with a huge robot from Morden Forces in the end.
Also, we wanted to have male teachers/instructors in Combat School mode so we could get more female fans for the franchise.
4) Are there any METAL SLUG game designs that had to be scrapped?
In order to create and release a game, tons of ideas or designs are born and destroyed.
Actually, in the first title, there was a stage that we had to redraw almost half of the background graphic because it ended up not matching our direction as development progressed.
So, it is hard to pick up one or two examples from them. But we did put excellent ideas in each game even if we had to change the design a bit here and there.
5) Who came up with Allen O'Neil and why does he keep coming back alive?
In the beginning, he was called 'a reckless soldier' and a character who rushed at characters by firing machine guns at random intervals. However, when we did this, there was no big difference between him and other tougher enemy characters. So we decided to create the current Allen (who is at least equal to the player characters - and may have more abilities) as a rival character who always creates a challenge.
The reason he is immortal is because he has a body of steel and guts. Also, he has to go home alive from the battlefield to be with his loving wife and child!
3. ART QUESTIONS
1) Are there any METAL SLUG tank designs that had to be scrapped?
There were a few scrapped when we were creating its concept designs. However, after we started creating their artwork and animations we used all of them. On the other hand, we used those already created and animated in-game by changing some specs or redraw some part if they didn't meet our current specs.
2) Are there any characters, locations, or villains that you enjoyed creating but were cut from a specific title?
'The next new stage is underwater city because we already created ground, space and underground stages!'
That was one of our ideas at that time. We had this underwater city where you could see fish men, but we had to cut it from a title because we could not put together the concept very well and did not have enough time.
If you are a big fan of METAL SLUG, you know there was one quick scene of this idea in the ending. We put that in for a hint to the sequel.
3) What are the 'secrets' to making such smooth sprite animations?
That's effort, spirit, guts and concentration! Also anger, sadness and obsession become energy fueling our sprite animations.
4) How do you maintain such a consistent visual style for the METAL SLUG series?
That is because our chief designer had a mental image for the visuals and it was conveyed to the other staff correctly, concisely and clearly. Additionally, we had to redraw the artwork if it did not meet a certain quality. Under some circumstances, he redid the artwork himself.
5) Who comes up with the wacky enemy designs?
The designers were told to just make plan rough animations and images. Basic art and animation moves for the enemy characters were
planned and designed mostly by the chief designer exclusively. That is one big reason why you can feel consistency through the series. After the basics were done, they were sent to other staff to add actual movement and animation patterns. In this process too, the impressive looking movements were born.
Also, lots of ideas for cool enemy characters that were thought up by our designers are in the games.