A digression in consideration of slivers
After I posted yesterday's discussion of Thallids, a brief discussion about it over IRC turned to another of Magic's iconic creations, the sliver.
Slivers are one of the more interesting things Magic has created. Their gimmick is that they rapidly evolve to take on new abilities and share those abilities with every other sliver in the area. In the CCG, that works well, because they start off small, and every sliver played increases the power of every other sliver on the table. While that's pretty cool and pretty evocative, they're annoying to play against and really wouldn't transfer to tabletop RPGs very well. At least...not directly.
The initial state in a game of MtG is a blank tabletop. Neither player begins the game with any resources in play. So when the first sliver is laid on the table it is done so in a void. It's the only one that is affecting anything. As the game progresses, more and more slivers are summoned and more and more abilities are passed to the hive, until each sliver is a powerhouse unto itself and the hive simply rolls over the opposition. (Ideally.) Since every sliver is clearly labelled and the ability it is sharing with the hive is clear, it's simple enough for an opponent to use removal cards on the slivers that grant specific powers and get them off the table.
The tabletop RPG encounter is almost the opposite of the above situation, assuming a direct translation of the cards to the tabletop. All the slivers are on the field at the start of the encounter, sharing their abilities with each other. In terms of distinguishing one from another that makes it difficult to tell which one is providing the ability to attack twice per round over which one is providing the vulnerability to lightning. You can take one out but it's anyone's guess what that does to them. Plus, when each one of the slivers is doing what all the others can do it gives them more versatility and power, and as each one drops that versatility and power goes away. The hardest to kill is the first to go, no matter what, because each death diminishes all the rest. By the last remaining sliver, there's very little of that power remaining, and it creates a challenge that in effect becomes dramatically easier the further along one proceeds.
In the card game, slivers represent a homogenous, rapidly escalating threat. The expectations of D&D call for an encounter to be filled with heterogenous monsters that retain a certain amount of stability throughout, and present clear tactics for the players to adopt. There's no way to create that kind of encounter with slivers in D&D if we simply try to duplicate exactly the way they are on the card, as we did with thallids.
So, to adapt them from Magic to D&D, we need to ask what it is that slivers do--what defines slivers as slivers. We need to examine ways in which we can adapt that and reflect it in a way that works within the mechanical framework of D&D. Finally we would decide on how exactly we want to represent that--that is to say, we would create stats for the slivers.
To begin, then, we examine sliveriness. Slivers are nifty insect dudes who evolve to suit their environment and share their adaptations immediately with the hive. That sharing of abilities is literally the only trait common to all slivers. At this point we don't really need to look at the cards anymore--there's enough abstraction in Magic that a lot of the abilities are difficult to translate, and there are enough ideas for adapting to the environment that it's relatively simple to create interesting and relevant sliver adaptations as needed to suit the campaign.
Next we need to determine the best way to represent their ability-sharing. The answer that immediately springs to mind is to treat it as an aura. Each sliver creature should have an aura that gives other slivers in that aura some measure of its abilities. That said, to keep the encounter heterogenous, the aura shouldn't transmit the full benefit of the adaptation, merely a subset. A sliver with resist fire 10 and a fire-based attack, for example, might only transmit resist fire 5 to other slivers in the aura and add the fire property to all their attacks. This ensures that each sliver can retain its own role in the encounter but benefits from the other slivers nearby.
After that we'd want to decide how this information presents itself visually. The fire sliver mentioned above might be deep, glowing red and radiate waves of heat. Slivers in its aura might take on a reddish tinge and become hot to the touch. A cold sliver could likewise be blue and covered in rime, and slivers in the aura would become coated in frost. This gives the players a visual cue to identify which sliver is the source of a given resistance or ability, separate from the mechanical.
Finally, we'd move to stat the slivers out. I would be inclined to place the slivers in paragon tier--while they would work well in just about any environment at mid to high heroic, the cumulative nature of their abilities and the danger they pose in fluff feels to me more in line with a paragon-level threat. I would also be inclined to create a baseline sliver, not necessarily as a template, but as something that would simply benefit from the presence of the more powerful varieties. Baseline slivers would even work well as minions--that way an entire swarm of them could accompany one or two different forms of the more advanced slivers.
I'm not especially interested just this minute in creating concrete stats for them beyond this point--you've seen how to do that already, and there are far too many good possibilities for sliver breeds to be adequately represented in the space here. Almost any template or ability possessed by any other monster could conceivably be added to a sliver, and transmitted in partial or lesser form to others. Poison, acid, fire, ice, lightning, thunder, psychic, regeneration, armored carapaces, speed, size, quills, defensive spines, tentacles, burrowing, flying, phasing--everything and everything. You could have slivers that explode when they die, or slivers that bleed acid.
The only thing that I would caution is not to overuse something like slivers. They're cool, they're fun, they're varied, but a bit more variety from time to time is never unwelcome. Nobody wants to spend their entire heroic career focused on one type of enemy, even if you as a GM spent a lot of time working on creating the stats for them.
Slivers are one of the more interesting things Magic has created. Their gimmick is that they rapidly evolve to take on new abilities and share those abilities with every other sliver in the area. In the CCG, that works well, because they start off small, and every sliver played increases the power of every other sliver on the table. While that's pretty cool and pretty evocative, they're annoying to play against and really wouldn't transfer to tabletop RPGs very well. At least...not directly.
The initial state in a game of MtG is a blank tabletop. Neither player begins the game with any resources in play. So when the first sliver is laid on the table it is done so in a void. It's the only one that is affecting anything. As the game progresses, more and more slivers are summoned and more and more abilities are passed to the hive, until each sliver is a powerhouse unto itself and the hive simply rolls over the opposition. (Ideally.) Since every sliver is clearly labelled and the ability it is sharing with the hive is clear, it's simple enough for an opponent to use removal cards on the slivers that grant specific powers and get them off the table.
The tabletop RPG encounter is almost the opposite of the above situation, assuming a direct translation of the cards to the tabletop. All the slivers are on the field at the start of the encounter, sharing their abilities with each other. In terms of distinguishing one from another that makes it difficult to tell which one is providing the ability to attack twice per round over which one is providing the vulnerability to lightning. You can take one out but it's anyone's guess what that does to them. Plus, when each one of the slivers is doing what all the others can do it gives them more versatility and power, and as each one drops that versatility and power goes away. The hardest to kill is the first to go, no matter what, because each death diminishes all the rest. By the last remaining sliver, there's very little of that power remaining, and it creates a challenge that in effect becomes dramatically easier the further along one proceeds.
In the card game, slivers represent a homogenous, rapidly escalating threat. The expectations of D&D call for an encounter to be filled with heterogenous monsters that retain a certain amount of stability throughout, and present clear tactics for the players to adopt. There's no way to create that kind of encounter with slivers in D&D if we simply try to duplicate exactly the way they are on the card, as we did with thallids.
So, to adapt them from Magic to D&D, we need to ask what it is that slivers do--what defines slivers as slivers. We need to examine ways in which we can adapt that and reflect it in a way that works within the mechanical framework of D&D. Finally we would decide on how exactly we want to represent that--that is to say, we would create stats for the slivers.
To begin, then, we examine sliveriness. Slivers are nifty insect dudes who evolve to suit their environment and share their adaptations immediately with the hive. That sharing of abilities is literally the only trait common to all slivers. At this point we don't really need to look at the cards anymore--there's enough abstraction in Magic that a lot of the abilities are difficult to translate, and there are enough ideas for adapting to the environment that it's relatively simple to create interesting and relevant sliver adaptations as needed to suit the campaign.
Next we need to determine the best way to represent their ability-sharing. The answer that immediately springs to mind is to treat it as an aura. Each sliver creature should have an aura that gives other slivers in that aura some measure of its abilities. That said, to keep the encounter heterogenous, the aura shouldn't transmit the full benefit of the adaptation, merely a subset. A sliver with resist fire 10 and a fire-based attack, for example, might only transmit resist fire 5 to other slivers in the aura and add the fire property to all their attacks. This ensures that each sliver can retain its own role in the encounter but benefits from the other slivers nearby.
After that we'd want to decide how this information presents itself visually. The fire sliver mentioned above might be deep, glowing red and radiate waves of heat. Slivers in its aura might take on a reddish tinge and become hot to the touch. A cold sliver could likewise be blue and covered in rime, and slivers in the aura would become coated in frost. This gives the players a visual cue to identify which sliver is the source of a given resistance or ability, separate from the mechanical.
Finally, we'd move to stat the slivers out. I would be inclined to place the slivers in paragon tier--while they would work well in just about any environment at mid to high heroic, the cumulative nature of their abilities and the danger they pose in fluff feels to me more in line with a paragon-level threat. I would also be inclined to create a baseline sliver, not necessarily as a template, but as something that would simply benefit from the presence of the more powerful varieties. Baseline slivers would even work well as minions--that way an entire swarm of them could accompany one or two different forms of the more advanced slivers.
I'm not especially interested just this minute in creating concrete stats for them beyond this point--you've seen how to do that already, and there are far too many good possibilities for sliver breeds to be adequately represented in the space here. Almost any template or ability possessed by any other monster could conceivably be added to a sliver, and transmitted in partial or lesser form to others. Poison, acid, fire, ice, lightning, thunder, psychic, regeneration, armored carapaces, speed, size, quills, defensive spines, tentacles, burrowing, flying, phasing--everything and everything. You could have slivers that explode when they die, or slivers that bleed acid.
The only thing that I would caution is not to overuse something like slivers. They're cool, they're fun, they're varied, but a bit more variety from time to time is never unwelcome. Nobody wants to spend their entire heroic career focused on one type of enemy, even if you as a GM spent a lot of time working on creating the stats for them.