Sliding scale TNs is what most people are familiar with; it is the system that was introduced in the first rpg. The TN changes depending on what type of armor and modifiers your target has. The better the armor the higher the TN (or lower – math was hard back in the ancient days). Add in such things as magical effects and ability modifiers and the TN was ever in flux.
4E took the concept of the sliding scale to its most blatant. Encounters and TNs are designed based on the level of the characters. Picking a lock as a level 1 character requires a much lower TN than picking a lock when the characters are at level 25. This was done intentionally to keep the characters challenged. This expanded outward and 4E had in place a system, in the form of a table based on character level (page 42), to scale each component of an encounter – AC, Fortitude Saves, damage dealt, damage threshold, etc. The table was a handy way to keep challenging the characters at all levels consistently and it did its job very well. Whether you wanted that level of scaled TNs and encounters is a matter of personal preference but 4E gave a very well done sliding scale, possibly the finest of any rpg to date.
The benefits of sliding scale TNs are…
-Encounters are easy to design as the scale required is all predetermined.
-Encounters will be a challenge regardless of character level or time played because the TNs are balanced.
-Players feel that their characters are gaining in power as they put out larger and larger numbers. It is a readily apparent character growth. “Look, I just did a new high number!”
Games with fixed TNs have a default TN that is set regardless of other factors. Savage Worlds is an excellent example of this. Savage Worlds has a default TN of 4. Whatever a character wants to do they must roll a 4 or more to succeed. Pick a lock with a Novice Rank character? The TN is 4. Pick a lock with a Legendary Rank character? The TN is 4.
The benefits of fixed TNs are…
-Encounters are easy to design as there is a baseline of expectation.
- Encounters will be a challenge regardless of character level or time played because these systems allow for limited inflation of character’s numbers.
- Players feel that their characters are gaining in power as they easily accomplish tasks that once were difficult. It is a readily apparent character growth. “Look, I just beat the TN by a new high number!”
As you can see, the benefits of fixed and sliding scale TNs are similar - just different ways of looking at the same thing. And that is because, ultimately, all TNs are sliding scale; the only difference is the direction of approach to the TN.
Even with a fixed scales TN, such as Savage Worlds, there are always modifiers that are applied to the TN and these modifiers scale with the level/rank of the characters. As character progress their modifiers increase in numeric value. Where before they gained a simple +1 to a die roll at 1st level for a particular ability/skill, they now gain an additional +2 from a couple of different feats or magic items(new gear) or level bonus or increased skill or a myriad of other character gains. In effect, this means the TN has decreased by the same amount. The powers the characters bring to a TN bring down its overall value.
Of course the reverse of this is also true. As the characters progress in power/ranks/level they inherently face tougher and tougher monsters – this is how a DM continues to challenge them. A campaign grows stale real fast if the characters continue to face the same adversaries time and time again. These higher level monsters come with higher defenses. Thus the modifiers the monsters bring to the table increase the TN. The powers the monsters bring to a TN bring up its overall value.
Ultimately this means that TNs stay roughly the same overall; the number needed on a die roll for a success remains approximately the same regardless of the level of the characters or adversaries. However, they are still changing and sliding based on the powers and levels of the player characters. So, which system works best; fixed TNs or sliding scale TNs? It really comes down to which feels best for the particular style/feel of the game.