Partly inspired by this post at Aeons & Auguaries I thought I'd share some thoughts about systems and conversions between them. Like JD Jarvis, I've run campaigns incorporating elements from lots of different games - in my case Runequest, MERP, WFRP and C&S spring to mind alongside the D&D/AD&D mashup that was my standard fare. Should I ever get round to running either my Golden Heroes or Star Frontiers campaigns, there will be plenty in them from Traveler, Marvel Super Heroes, Call of Cthulhu, Judge Dredd Role Playing, Gamma World, Doctor Who, Paranoia, Heroclix gaming and all sorts of other places.
I was thinking recently about 'conversion' from one system to another and I think 'style' is more important than substance. When I was adding such things to my D&D games, I tried at first to convert things closely but then gave up. Now, I've got a bunch of charts about how to convert 3d6 abilities to a 2d6 format or a percentage system, but in the end, a Trollkin is pretty much the same a Goblin, a Dark Troll is basically a Hobgoblin or maybe like a Gnoll. So does it matter about strict mathematical conversion? Apart from anything else, that requires some complicated work on how abilities actually function in different gaming systems.
I'm not familiar enough with MERP or Runequest to do those conversions 'accurately' and I couldn't even hope to start with C&S or WFRP - except by getting a feeling for what supposed to be happening and transposing the feel. Is the wild boar special? No; in which case I'll use an average wild boar in D&D. Is the trapper really an expert swordsman or anything? Doesn't seem to be, but he has the feel of someone who isn't a complete pushover, so I'll give him a Fighter's stats but only arm him with a staff and a dagger and say his jacket counts as leather. Are the cultists at the inn really powerful? No, but there's a couple of them know how to fight and one is a coven leader, so I'll make that 3 Normal Men, 2 1st Level Fighters and a 2nd Level Cleric.
In thinking how to stat 'The Hulk' for D&D recently, I came to the conclusion that there was no way I was going to find some official Marvel stats and try to do a straight conversion. Instead I decided to explain what I know about the Hulk in D&D terms. As Bruce Banner is a scientist, he would be a sage (probably; possibly even a Magic User) who is under a curse that means in certain conditions he transforms into a large, strong, angry humanoid that is capable of taking an extraordinary amount of punishment. So I decided he is a kind of Were-Troll (I could have made him an Ogre but I like the idea he regenerates) - when he's 'stressed' either through taking damage for the first time, or in a situation he finds it difficult to deal with, he has to make a WIS roll. Failure means he transforms into a troll for 7-12 turns or until rendered unconscious (eg by a Sleep spell or similar).
It's not exact but it fits pretty well as an explanation of what's happening, in terms that the D&D system understands. The players do it all the time anyway - when my party found a scroll with a Web spell on it, they described the Elf who cast it as 'Spiderman'. Why not? Maybe Spiderman, in D&D terms, has the ability to cast Web a bunch of times per day.
There is a different possibility of course - that I could get a bunch of special rules together and create an entirely new set of stats for a Hulk. But even then I think I'd probably end up trying to find a D&D analogue. Maybe he's a magic berserker? Well, thinking that has certainly made me remember that I included Slaine mac Roth in one of my games, who can perhaps be regarded as a pre-historic Hulk. Not that he's a physicist the rest of the time of course. But maybe looking at Berserkers would be another way to take this.
But maybe there is a way to do it. OK; for D&D, the special rules could work something like this. Bruce Banner has 4hp - he may not fight much but he's reasonably fit as a human, so I'll give him the maximum allowed by his class. The Hulk's special ability could be that any attack that doesn't reduce his hp to 0 in one go, adds that damage to his current hp, up to 18hp total (average basic points for a 4th Level Fighter or 'Hero'). Once he has acquired 1 extra hp, he counts as a 2nd-level fighter, once he's reached 10 hp, he counts as 3rd Level, once he's reached 14hp, he counts as 4th. He also uses his current Fighter Level as a strength bonus for melee combat - so if you hit him, he's going to get stronger and better at hitting you, until he's gone beyond maximum human strength, which seems reasonable enough.
I don't know if that is any better than making him take a WIS roll to become a Troll, though.