The Sentinels of the Multiverse card game has mechanics for some heroes and villains being each other's nemeses thanks to long-standing enmities between them built up over time. Nemesis status is reciprocal, and makes both more effective at opposing one another. The SCRPG currently lacks anything similar, but people do keep asking about it so here's a set of suggested house rule to emulate the card game mechanic. I've had to be a bit wordy to cover all the possibilities but the basic mechanic is very simple - nemeses each generate a free bonus each round that they can only use to mess with each other.
How Do I Get A Nemesis?
At the end of any session where a hero defeated or was defeated by a villain, the GM and the player involved may agree that the defeat has started a Nemesis relationship between the two. This is entirely optional and should be reserved for particularly galling or humiliating losses, particularly ones where some major scheme was thwarted or mortal insults exchanged. Both the GM and player can unilaterally veto the proposed relationship, never force someone to engage with these mechanics if they don't want to. While there are mechanical effects the main goal of having a nemesis is to offer more narrative roleplaying opportunities in future stories.
Once a Nemesis relationship is agreed to, it should be recorded on both the hero and villain character sheets, starting at a +1 Nemesis bonus.
For ex, after Doctor Atomico delivers a particularly humiliating drubbing to Shatterfist the super-mobster swears vengeance on him, vowing to pay him back tenfold and adding Nemesis (Doctor Atomico) +1 to his sheet. Our nuclear hero begins to take a personal interest in the villain's future schemes and likewise adds Nemesis (Shatterfist) +1 to his sheet.
What Does A Nemesis Bonus Do?
In any action scene where both nemeses are present and active, each of them generates a Nemesis bonus for free at the start of each of their turns as long as they don't currently one. This prevents you from stacking up several of them over multiple turns.
If interacting with your nemesis outside of an action scene where you don't use the scene clock, simply apply Nemesis bonuses to any Overcomes you make that are directly involved with your opposite number, as per the rules below. It's very common for fights to break out between nemeses during social or even montage scenes, starting an action scene on the spot.
Nemesis bonuses can be applied to the effect dice of any Attack or Hinder targeting the nemesis. If an Attack or Hinder includes multiple targets, the Nemesis bonus will only apply to the nemesis target while the rest are affected normally.
Overcomes that the GM agrees are directly affecting the nemesis or foiling their current efforts can also benefit from a Nemesis bonus. In general it should apply to things like dealing with a challenge caused by the foe, such as escaping from one of their deathtraps or disabling some mechanism that's key to their goals in the scene, but not to environmental challenges, challenges created by allies of the nemesis and similar complications.
A character stops generating Nemeses bonuses if their opposite is defeated or leaves the scene. Incapacitated heroes do still get their bonus if their nemesis is still present and active, which can be used only to augment their Out ability. This gives heroes a slight edge over villains, who lack Out abilities.
How Many Nemeses Can I Have?
A hero can have multiple Nemesis relationships, each of which is tracked separately. I'd strongly recommend limiting them to a maximum of one per collection, representing more veteran heroes gradually building up more villainous grudges over time and developing their own Rogues' Gallery of recurring villains. Villains don't have limitations on how many heroic nemeses they may have ta the same time. Some exceptionally vindictive villains may consider an entire opposing team to be nemeses, but they track the relationship with each hero independently.
If a hero or villain has multiple nemeses in the scene, track each one's bonuses separately.
How Do Nemesis Relationships Change?
After each session in which a nemeses pairing faced off against one another at least once, increase the relationship bonus by +1 to a maximum of +5. This doesn't have to be in an action scene, although fights do tend to break out between nemeses easily so pure social scenes are rare.
If both player and GM agree that a Nemesis relationship is getting stale or starting to matter less over time, reduce the bonus by one instead, removing the relationship entirely if it would drop below +1. Sometimes what looked like a fun story idea just doesn't work out, and "breaking up" with an old nemesis makes room for a new one.
If a villainous nemesis dies, switches sides from villain to hero or leaves the campaign entirely, the relationship ceases to count against the maximum number allowed to their heroic counterpart. If (as often happens in comics) the former nemesis reappears as a villain, the relationship can be reactivated if both GM and player agree it would still make for a good story. If not, simply remove the relationship altogether, as the radical changes involved mitigate the usual "cooling down" period above.
If a hero undergoes death, retirement, or otherwise ceases to be an active PC their villainous counterpart generally erases the Nemesis relationship. If both the player(s) involved and the GM think there's a good story to be had they might instead shift the relationship to a new hero, perhaps either a teammate of the departed nemesis or a new hero connected to their legacy.
Design Notes
Always remember that the main purpose of having a Nemesis relationship is to add narrative opportunities to the game. While the bonuses involved are meaningful they also balance each other out, and aren't something to chase after just for power. These rules are meant to create stronger connections between heroes and villainous NPCs and help build a roster of returning foes the players can invest some emotion in foiling at every turn.
