While I haven’t been in the RPG community for as long as many, I’ve had the opportunity to play and run a huge variety of systems. I’ve found that most systems have an idea that I always miss when I’m playing any other game. Like spending an XP to reroll my dice when I’m not playing a Cypher Game, or the duel Sanity/Stability system in Trail of Cthulhu. Unfortunately, moving a lot of these mechanics to a new system isn’t possible without re-writing the system, and work instead to be something that makes returning to that system every time we sit down to play. However, I think there are some ideas out there that could be moved to different systems with a little effort.
The warband in my Dark Heresy campaign is trying to learn more about a possible heretical figure in the Inquisition. When plotting out the arc of the campaign I knew I wanted them to be able to climb their way up a chain of command that could offer them more information as they revealed the scope of their adversaries’ influence. There isn’t a ready way to build this sort of conspiracy out in Dark Heresy, but there is the Conspyramid in Night’s Black Agents. Night’s Black Agents is a great game for conspiracy and investigations, and gives tips to the GM to build out their own network and bureaucracy that’s working against the players. This allows the GM to have an easy to reference chart that lets them track the intricacies of connections all leading to the person at the top of the pyramid, the big bad that your players are going to want to take out. Aser’s Conspyramid in our NBA game was something we slowly discovered and worked through for the entire campaign, finding more and more connections wherever we looked. Using the conspyramid doesn’t need to be that expansive though, maybe your investigators only need to investigate the local mob, or a faerie court. The system Kenneth Hite put together is flexible enough for you to be able to build a great spine for your adventure in any system. It also provides an easy measure for when and how to scale up the resistance your players encounter as they work their way towards the truth and their inevitable doom.
Failed rolls are disappointing in any game, and a lot of systems now include ways for you to reroll your dice. My favorite of these is from 7th Edition of Call of Cthulhu: pushing your roll. When you fail a roll in Call of Cthulhu, you have the option to reroll the die, with a narrative explanation of how you’re trying harder or differently to complete the task. What I love about pushing your roll is that failure carries much more dangerous consequences then just not completing the task. For example, one of my players tried eavesdropping at a door and failed to hear what was happening. When he pushed his roll and failed again, his character not only failed to overhear what was happening in the room, but accidentally opened the door and let his targets know he was there. This mechanic is something that could be easily added as a home rule in any system. There are limitations on when you can use it in Call of Cthulhu, and if you’re going to pull into your game you should look into maintaining that sense of balance. However, if your players are failing often, or you want to add another opportunity for things to go wrong for them, this is a great rule to add.
Another way to get around disappointing rolls is to not require them. Which sounds crazy, but is a mechanic that I like in Trail of Cthulhu and Delta Green. However, the point spend in Trail of Cthulhu isn’t something that is easily transferred to other systems, so I’d recommend looking into the way Delta Green treats skills. As a d100 game, you’re able to get a pretty high ranking in a lot of skills, and that represents a huge investment in time and willpower for your character. So, for certain tasks and in certain circumstances, Delta Green will allow characters to automatically succeed if their skill is high enough. Which means your biologist isn’t going to fail to do some research on a bacterial strain, or your IRS agent is going to be competent at opening up QuickBooks for a glance at company finances. Moving this over to a non-d100 systems means you’ll need to pick different thresholds at which you’ll allow a skill to succeed automatically. Maybe if your Cleric has a +10 to Knowledge: Religion, they won’t need to roll to know the name of the god whose temple you’re currently looting.
Most of these rules exclude re-rolling or automatically succeeding in combat. However, sometimes your combat drags on and you still can’t seem to hit. 13th Age has a really nice mechanic called the Escalation Die, which starting on round two allows the PC to add a bonus to their attack rolls to make it easier for them to hit. This mechanic allows your players to hit more frequently as a battle progresses, meaning that combat will conclude more swiftly. This mechanic specifically would be helpful in a d20 game, where small bonuses could mean the difference between hitting and missing. For something like Gumshoe or Warhammer 40k, you would have to alter how that bonus is determined, or how frequently it is increased.
Core books for systems you aren’t playing can still provide a treasure trove of inspiration and resources that you can use to improve your own game, or make parts of the system that irritate you a little easier to deal with. I always keep my eye on sales at DriveThruRPG, or the games available at the Bundle of Holding to get access to new systems at great prices. If you’re interested in any of the mechanics I mention here, I highly recommend picking up the system they come from to learn more about the specifics for integrating them into your own game.