A simple-but-effective way to challenge the heroes is to use skill penalties. Many tasks in GURPS recommend a wide variety of penalties to cover less-than-ideal conditions, exceptionally tough opposition, etc. Looking up and assessing these penalties can be time-consuming, however. When the team is poised to blow the vault door or raid the villain’s mansion, it’s boring and frustrating for things to grind to a halt while the GM consults rules and tallies modifiers.
As an alternative to detailed modifiers, the GM can set a single difficulty – the Basic Abstract Difficulty (BAD) – that covers all aspects of a particular phase of the adventure. This is simply a penalty from 0 to -10 that replaces detailed situational modifiers. The only other modifiers that apply are those that the PCs bring into the picture: bonuses for equipment, penalties for disadvantages, etc.
Example: The heroes are infiltrating a secret base. The GM feels it should be tough, so he assigns a BAD of -5. Rolls to climb walls, pick locks, disarm alarms, and so forth are thus at -5 instead of taking detailed modifiers for things like security system quality and the compound being situated in an icy wasteland. If the squad brings fine equipment that gives +2 to skill, though, then that modifier still applies.
The GM can revert to detailed modifiers whenever he wants, such as for important special cases, random occurrences that aren’t tied to the adventure, or events that would genuinely benefit from a dramatic pause. The goal of BAD is to estimate an adventure’s challenge level and save time when details matter less than flow – not to supplant the GM’s judgment.
The GM can pick whatever BAD “feels right.” When rating how challenging specific opposition is, though, he might opt to calculate it as follows: Rate the adversaries’ basic point value as an Enemy, divide by 4, and drop fractions.
Example 1: Early in an adventure, the heroes are tracking down a corrupt detective. An ordinary cop is a -5-point Enemy, for a BAD of -1. Rolls to gather evidence against him, search his home, and so forth are thus at -1, representing his connections and attention to security.
Example 2: Later, the team has to take on the rotten cop’s entire department! That’s a -20-point Enemy, so BAD is -5. This affects rolls to evade security at the station, talk a neutral NPC into helping out, and so on. It represents the fact that there are lots of cops, with good gear and significant social clout.
As the above examples suggest, BAD need not remain fixed for the entire adventure. Part of the action-movie formula is that challenges mount as the plot unfolds: the closer the heroes get to the boss, the worse BAD gets.
The PCs can also worsen BAD without the bad guys’ help! Exploits offers many rules for avoiding ill-advised violence, hiding corpses and evidence, and so forth. If the heroes ignore these and blast through the adventure, leaving a trail of blood and burning wrecks, then the GM may dial up BAD to reflect the authorities or the team’s own bosses making their life harder.
However, BAD doesn’t always get worse. If the crew scores a coup – e.g., steals files containing the names of the corrupt cops and the technical specs for the station’s security system – then the next part of the adventure might be easier. This is a fitting reward for a clever plan or a timely critical success.
The PCs will often meet their opponents in Quick Contests. Every +1 to their rivals’ skill is +1 to the bad guys’ margin of success – which has the same effect as giving the heroes -1, just like incrementing BAD by -1. Thus, when the squad faces henchmen (not mere mooks) directly, the GM may wish to increase the NPCs’ skill instead of applying BAD to the heroes’ skill.
At the GM’s option, henchmen without character sheets have an effective skill of 10 + absolute value of BAD: 11 at -1, 12 at -2, and so on. As with all BAD things, this is abstract. Actual skill, equipment quality, extra time, and anything else that might matter is all rolled into one handy number.
The GM shouldn’t use BAD in combat or chases. The goal of BAD is to abstract things like enemy planning, security systems, and social connections – not battlefield or road conditions, never mind the PCs’ tactical options. It’s fine to use BAD to rate a henchman’s skills in one of these situations, however.