Friday, August 29, 2008

Difficulty Design: A Difficult Endeavour

Designing and tuning game difficulty is trickier than it may seem. I'll try to make this one as concise as possible.

For some background material, consider looking into Flow in Games: A Jenova Chen MFA Thesis, and Gamasutra's Game Design Essentials: 20 Difficult Games.

Today I going to highlight a few methods of creating game difficulty/challenges.



ORGANIC METHODS

Optional routes/objectives: Super Mario Brothers Coins. As the player moves through each level, there are coins that are never placed in the player's "laziest" path to the goal. To nab these coins, players must jump for them which often requires the player to deviate from the efficient linear path to the end of the level. Some coins are much harder to obtain than others. Because every coin the player sees can be grabbed in a single pass through a level, the boundaries of the challenge are set. In this way, the coins that are placed in tricky areas over dangerous hazards or endless pits communicate a level of difficulty to the player. At any time, the player can accept the challenge and go for the coins, or skip them all together. After all, they're optional.

Adjustable Pacing: Super Mario Brothers RUN mechanic. There are few jumps in this game that require the player to get a running start to overcome. This design choice makes the RUN mechanic largely uneeded for beating the game. Aside from how the RUN mechanic increases Mario's maximum JUMP range vertically and horizontally, by running players can increase the pace of the game which in turn increases the difficulty. This is the primary function of the RUN mechanic. When running, the screen scrolls faster to keep up with Mario. Because the screen scrolls faster, the upcoming platforms, obstacles, enemies, and other hazards move toward Mario more quickly giving the player less time to react. Having less time to react creates a more difficult game experience.

Adjustable/Optional upgrades: The Legend of Zelda heart containers. In this game series, players are rewarded for defeating bosses with full heart containers that extend Link's maximum health by one heart. The more hearts Link has, the more hits he can take before falling. On the other hand, if the player wants to make the game more difficult, they can leave the heart continers behind and continue on with their adventure. Playing Phantom Hourglass from start to finish with only 3 hearts was more difficult than I expected. I found that I had to buckle down and focus to stay alive instead of goofing off half of my health like I normally do in Zelda games. The best part about skipping these heart container upgrades is, true to their organic design, the containers remain where they are left giving the player the ability to go back and collect the containers to make things easier for themselves.


INORGANIC METHODS

Leveling Up: All RPGs where enemies don't level up with you. This one is pretty obvious. If your enemies are at level 5 and you can't beat them at level 3, leveling up until victory is possible is the common course of action. But, if at any point the player doesn't feel like leveling up (or leveling up too much), they can always take on the challenge and attempt to squeeze out a win by any means possible. It's all about numbers and managing that spread sheet style, optimization, attack-attack-heal gameplay. I remember playing FF12, Pokemon Diamond, Valkyrie Profile, and Fire Emblem severely under leveled. To come out on top, I had to pull out all the stops and exploit the "spread sheet" and healing abilities to the max. Needless to say, it was difficult.

Optional use of items (especially heal items): Boktai, Ninja Gaiden, BioShock, Resident Evil Series, Zelda series, MGS series, etc. In these games, when you're low and health and you don't feel like dying, healing items are just a few clicks away. Whether the healing items are reached through menus or via a specific button, as long as the player has healing items/abilities he/she can heal to extend their health. Purchase a "lives of a thousands gods," a take 2, or capture a fairy in a bottle and upon losing all of your health, your character will spring back to life for a second shot at victory. The more of these specialty recovery items the player has, the easier the game becomes. It's all up to the player to adjust as he/she sees fit. And it's not just healing items. Other items/abilites adjust the game difficulty by boosting strength, speed, defense, and other attributes.


MODAL METHODS

Most games address the difficulty issue by giving the player the option of selecting a mode of play with varrying levels of difficulty. The common term for such a mode is "hard mode." Viewtiful Joe takes these modes to an extreme even for Capcom: Kids (easy) Adults (normal) V-rated (hard) and Ultra V-rated (super hard). Super Smash Brothers Brawl also features a variety of difficulty modes.



In a hard mode the difficulty is increased by manipulating any number of the following factors.
  • Player health/enemy strength
  • Enemy types
  • Number of enemies/hazards
  • Upgrade requirements (more money, experience points, kills, etc.)
  • Item prices
  • Time limits
  • New/expanded objectives & challenges


The game that I feel does the best job with the modal method of game difficulty is Perfect Dark. From Agent, Secret Agent, to Perfect Agent, a number of factors are tweaked to tune the game difficulty so that the core design is maintained. This in itself is hard to do, but in addition the 3 modes are designed so that each mode is unique while building up the player's knowledge so that everything comes together when playing on Perfect Agent, the hardest mode.

Compared to the Agent and Secret Agent, Perfect Agent changes the following factors:
  1. Enemies are more accurate and have stronger body armor. The defensive upgrade makes limb shots less damaging, yet shots to the head and chest are still just as effective. At the same time, enemies still flinch and recover from shots in the same way they do in the other difficulty modes.
  2. Shields (defense upgrades) are removed from the maps.
  3. Additional mission objectives are designed into Perfect agent compared to Secrete Agent. With each additional objective, the strategies, abilities, and routes of play change significantly. For example. in the fourth mission, instead of saving a hostage from afar with sniper support, in Perfect Agent the player takes up the role as the hostage only to break out from capture. Though the majority of the mission objectives are the same as from Secret Agent, tackling the objectives from the inside of the compound is like playing a completely new level.


Another game that did a good job making each difficulty level unique so that even players who are skilled enough to take on the hardest mode have a reason to play the easier modes is Ikaruga.


DESIGN PROS

Designing game difficulty organically has a lot of design pros.
  • The added challenges are created out of concrete mechanics. Adhering to form fits function is always a plus.
  • The forms and functions remain stable. All the moves, characters, objects, and enemies always consistently reflect the same values and mechanics. Enemies won't be stronger or weaker depending on the mode.
  • Because everyone will gather their knowledge from the same experience, everyone will be on the same page. This allows players of different skill levels to relate to each other and compare.
  • The player has the power and the flexibility to organically adjust their difficulty level up or down in real time. This ability becomes a vehicle of the player's self expression.

Unfortunately, the inorganic methods increase the level of abstraction in a game's core design. The biggest benefit of the modal method is that players don't have the ability to wimp out and adjust the difficulty level back down to easily get around tricky challenges. For the most part, once you select "hard mode" you're stuck and there's no going back. It's like jumping off the high dive or strapping yourself into a roller coaster ride. Many gamers don't want to option to chicken out because they know they'd either take it or dwell on the choice. Also, though the organic method is a mode of expression, the modal method is a clear way to communicate a minimum level of accomplishment.

Personally, I like a nice mix of organic and modal difficulty options. And on that note, I despise the option to change the difficulty setting at any time in a game. BioShock. Tales of Symphonia. The World Ends With You. I'm looking at you!

2 comments:

Bryan said...

Didn't Super Mario Bros. have secret warps to later worlds? Didn't Super Mario Bros. 3 have warp whistles and a map that allowed you to skip levels?

This seems a little inorganic, at least, more inorganic than the coin method is. On the other hand, it grants the player a lot more freedom and creativity in terms of difficulty.

Disgaea, which I've been playing for a little bit now, is heavily stat based and inorganic. It does have difficulty adjustment, but you have to use it outside of battle and it costs a trivial amount of influence to apply. What makes this interesting is that you can go through 10-level segments for bonuses where you can't adjust the difficulty. You can drop out early, but you can't do so too often, because the only way you can get more of the item is by finishing a 10 level segment. Disgaea does allow you to return to your previous position in the 10 level segment and finish it out.

The recent Sid Meier's Pirates! game includes several extremely organic difficulty adjustments with appropriate bonuses for each. You choose a beginning country and time period, each with their own splits of territory and ship types. You can change country (and help multiple countries) throughout the game by how you deal with them. You can bring on extra crew, which acts as a more organic HP bar, but the more crew you have, the harder it is to keep them happy and away from mutiny. You can choose an outright difficulty level, which makes missions, minigames, buying goods, finding treasure more difficult, and makes your crew more likely to mutiny, but significantly increases your share of the loot when you take a break and pay your crew. You have the choice to buy items which make the game easier, or ignore them, like the hearts in Zelda. They aren't as easy to come back to though. Lastly, most of the minigames vary in difficulty and you can avoid the most difficult versions if you don't feel ready.

KirbyKid said...

@Bryan

Congrats. You uncovered the secret difficulty topic I left out of the main article.

Yes. Warp pipes, warp whistles, clouds, keys and other methods for traversing the world map allow the player to fine tune their own progression through what would otherwise be a very linear game.

By skipping across worlds in Super Mario Bros, players get to the end of the game faster, but at the same time, skip precious 1ups and coins in the process. It's a bit of give and take on this one. Having the choice of which world to travel too helps the player adjust their experience as well.

Also, in Bros.3 the warp whistle has its limitations. When players warp to the "warp world" the available worlds they can travel to are limited to groups. The cloud is the same way, you can skip over one level, but if you don't plan your route carefully, you might end up having to play that level to progress in the end.

Indeed, these mechanics/abilities seem more inorganic than going for coins. However, instead of treating the levels as the "real game" and the world map as a glorified menu, if we give equal weight/significance to each using items such as the cloud or whistle on the world map becomes a legitimate mechanic. Sure, moving around the map isn't the primary mechanic of the game, but that doesn't mean it's not a worthy part of the whole. Because all of these options are contained within the game's mechanics, I'd have to say that they're all quite organic.

Good comments on Disgaea and Sid Meier's Pirates.