In our upcoming 3.20 expansion, Archnemesis will be replaced with a system that is more similar to the way monster mods worked in the past.

The issues that players often had with Archnemesis were:

• The keyworded mod names were not fully descriptive of what they did
• The mods often had multiple effects bundled which made them harder to understand
• Due to how many effects were included in a single mod, it made too many encounters too complex
• The way Archnemesis rewards were set up meant that many players felt like they couldn't just kill a monster, they had to consider if they wanted to bring a magic find character in to maximise rewards

The goals of the new system are:

• Mods do one specific thing
• Mods say what they do rather than having a thematic name you must learn and remember
• Encounters are simplified on average while retaining interesting fights
• Players are no longer required to do annoying actions to maximise rewards

Let's examine those goals individually:

Mods do one specific thing

Here's an example: The Magma Barrier Archnemesis mod did a whole lot of stuff. It started by putting a magma barrier around the monster, but it didn't stop there. It converted some of the monster's physical damage to fire damage, it added some extra fire damage on top, it granted fire resistance to the monster and it gave some physical damage reduction for good measure. It also spawned volatile flamebloods to follow you. The new equivalent modifier just puts a magma barrier around the monster and does nothing else.

Mods say what they do rather than having a thematic name you must learn and remember

For example, rather than "Incendiary", which broke down into six properties, you'd now see monsters with either "Ignites" or "Fire and Ignite Resistant". Instead of "Deadeye", which did five separate things, you'd now see "Applies Random Mark", "Extra Crits" or "Accurate" as separate unrelated mods.

Encounters are simplified on average while retaining interesting fights

The pool of mods that involve complex interaction (like spawning volatiles or ground effects on death) have been heavily diluted by the presence of the simpler mods. This means that you encounter more complex fights less frequently. But interesting and challenging emergent behaviour from overlapping mods can still happen, just less often.

Players are no longer required to do annoying actions to maximise rewards

In Archnemesis, rewards were associated with individual mods. This meant that you could tell what kind of rewards you would get in advance. In some cases, you were then effectively required to fetch a magic-find culling character to make sure that you maximised the value of the monster mod that you had found. In other cases, you would ignore a monster completely if you knew that it would only drop rewards that were of no value to you. In the new system, we have added a significant pool of new rewards to rares, but the reward that is on the monster is hidden (and not associated with a specific mod), so you don't know what kind of rewards you will get until you kill the monster. Rare monsters with more mods are more likely to have these special hidden reward mods. This new reward system smooths out the spikiness that the Archnemesis reward system had.

Conclusion

The original motivation for developing Archnemesis was that the previous monster mod system was very out of date. Many of the mods didn't have any appreciable effect under modern balance and there wasn't a lot of interesting gameplay possible. In our opinion, Archnemesis did succeed at adding a lot of interesting new mechanics to rares, but introduced the problems described above. While creating the new monster mods described in this article, we were careful to retain most of the interesting mechanics that Archnemesis introduced, but in a way that doesn't include a grab-bag of other effects and is diluted by many other simpler mods.

The result is a system that is very similar to what monster mods used to be like, but with much more up-to-date content and balance. Mods are simpler and say exactly what they do. While you can certainly still rarely encounter scary combinations of mods that really wake you up, it's a lot rarer than it was under the Archnemesis system. We feel that the new system is more modern and interesting than the old monster mod/nemesis system and is clearer and easier to understand in the heat of combat than Archnemesis was.