I think crossovers work best when they are roughly balanced, or told solely from the weaker side. Otherwise, except in the hands of the most skilled, they too often share the faults of the worst SIs; godlike characters/ships riding roughshod over the locals, solving all the perceived problems of the subordinate universe with a deus ex machina, etc.
Also, a level playing field makes for better character interplay, since they meet as near equals.
Bearing this in mind, I'd begin by saying the Trek and B5 universes don't have the same physical laws. The differences are unnoticable in everyday life or within the domain of currently known physics, but it does affect ultratech.
Warp drive, subspace, and related technologies, including shields, simply don't work in the B5 universe, at least not for the intended purpose. They might start radiating neutrinos, or telepathic static, or they might just melt to slag, but they cannot be made to work by Trek rules, even if 10,000 Scotts laboured for 10,000 years.
Where B5 tech is better, of course, the Trek tech might find its performance improved because its no longer trying to walk uphill in the teeth of a blizzard. Similarly, if B5 moves to the Trek universe. Another advantage is, Q can't exist in the B5 universe or Vorlons in the Trek uinverse, it would be like trying to run a Windows program on Linux, without a emulator.
(Emulators are possible, metaphorically, but only if you understand pan-dimensional physics well enough to hack the machine code, and even the Q don't play in that league. There may be other ways to finesse the technological incompatibility, but they are, at best, only a little easier, and they all have drawbacks]
Choose the damage levels carefully, and this puts the Enterprise on a par with the B5 ships. They won't be able to rely on their big guns to solve all the problems; they'll have to talk, which means plenty of juicy character interaction.
[It might seem the Enterprise has nothing useful left to offer B5, but they'd still have artifiical gravity, the universal translator, and other peaceful technologies. More importantly, they'd have a fresh approach, unclouded by Vorlon meddling.]
You can probably get a few chapters of material out of the Enterprise crew adjusting to their damaged ship, and their slow realisation that many of its systems are incompatible with this new universe. Then, after a month at impulse, they limp into B5, giving them a new set of challenges - lots of material for character exploration there.
Once you've set the stage, of course, you need a villain, but all the major Trek and B5 races have been used. You can either transplant a hostile race from some other source, saying it was in the B5 universe all along, or you can use villains with some dimension-hopping powers.
One among many such possibilities is the Cthulhu mythos.
Cthulhu and friends can easily be retrofitted into any universe, and they are recognisable major villains.
When the first ones were young abominations walked the stars, creatures that should not be.
Not all seas are of water. From the hyperspatial abyss that underlies the sea of stars were the elder gods born, in a time that might be the distant past, or the far future, for in those depths, deeper than the first ones dared plumb, time runs strangely. There are currents, the mad seers claim, that can sweep ships across the sea of time, and there are cities built to an alien geometry. [Which all means the elder gods can be both older and younger than the first one.]
In those cities dwell the elder gods, and their servants, chief among them their high priest Cthulhu and his star spawn. Now, those dread cities are rising from the depths, casting a shadow before them.
The telepaths are the first to sense it, their minds filling with visions of the elder gods, visions that leave even the strongest gibbering wrecks. A few, such as Spock and Bester, will eventually manage to pull themselves back to some semblance of sanity, though their eyes will ever be haunted, but most will never recover. Most had their minds utterly shredded in the first milliseconds of contact.
Knowing what is coming, the Shadows and the Vorlons abandon their plots and flee. With no one pulling the strings and the telepaths all mad, the B5 universe lurches to total war while paranoia runs rampant.
Next, the shadow of the elder gods, creatures that do not belong in any rational universe, warps the very structure of space and time, creating temporal anomalies and dimensional gateways, which is when the Enterprise enters the scene. [It's best if both the Enterpise and the villains arriving together is not a coincidence.]
Naturally, people will blame them for the problems, accusing them of being the scouts for an invasion. Resolving that allows for plenty more character scenes.
Then the slave races of the elder gods arrive, rising out of hyperspace to lay planets waste, starting with the weaklings who actually need ships, followed by wave after wave of stronger races, until come Cthulhu and his peers, any one of whom can destroy a planet bare-handed, and after them, the elder gods themselves. This allows for a lot of thrilling battle sequences.
Ideally, our heroes will stop the invasion before the elder gods arrive. Once they've worked out they're all on the same side, they'll need to work out what's going on, then venture into the depths of hyperspace themselves (for which, conveniently, the Enterprise happens to be well suited) and confront the elder gods in their eldritch city even as the final battles rage in the normal world, a thousand last stands.
Winning won't be easy, but if it was you wouldn't need heroes to do it. Great heroes need great challenges to show their mettle, which is why triumph over adversity is a classic tale. It's also why easy victories make for weaker stories.
You can tell the same basic story with many other villains, of course. Nor would it change much if they were invading from other dimensions rather than from some hidden recess of the B5/Trek universe.
Also, a level playing field makes for better character interplay, since they meet as near equals.
Bearing this in mind, I'd begin by saying the Trek and B5 universes don't have the same physical laws. The differences are unnoticable in everyday life or within the domain of currently known physics, but it does affect ultratech.
Warp drive, subspace, and related technologies, including shields, simply don't work in the B5 universe, at least not for the intended purpose. They might start radiating neutrinos, or telepathic static, or they might just melt to slag, but they cannot be made to work by Trek rules, even if 10,000 Scotts laboured for 10,000 years.
Where B5 tech is better, of course, the Trek tech might find its performance improved because its no longer trying to walk uphill in the teeth of a blizzard. Similarly, if B5 moves to the Trek universe. Another advantage is, Q can't exist in the B5 universe or Vorlons in the Trek uinverse, it would be like trying to run a Windows program on Linux, without a emulator.
(Emulators are possible, metaphorically, but only if you understand pan-dimensional physics well enough to hack the machine code, and even the Q don't play in that league. There may be other ways to finesse the technological incompatibility, but they are, at best, only a little easier, and they all have drawbacks]
Choose the damage levels carefully, and this puts the Enterprise on a par with the B5 ships. They won't be able to rely on their big guns to solve all the problems; they'll have to talk, which means plenty of juicy character interaction.
[It might seem the Enterprise has nothing useful left to offer B5, but they'd still have artifiical gravity, the universal translator, and other peaceful technologies. More importantly, they'd have a fresh approach, unclouded by Vorlon meddling.]
You can probably get a few chapters of material out of the Enterprise crew adjusting to their damaged ship, and their slow realisation that many of its systems are incompatible with this new universe. Then, after a month at impulse, they limp into B5, giving them a new set of challenges - lots of material for character exploration there.
Once you've set the stage, of course, you need a villain, but all the major Trek and B5 races have been used. You can either transplant a hostile race from some other source, saying it was in the B5 universe all along, or you can use villains with some dimension-hopping powers.
One among many such possibilities is the Cthulhu mythos.
Cthulhu and friends can easily be retrofitted into any universe, and they are recognisable major villains.
When the first ones were young abominations walked the stars, creatures that should not be.
Not all seas are of water. From the hyperspatial abyss that underlies the sea of stars were the elder gods born, in a time that might be the distant past, or the far future, for in those depths, deeper than the first ones dared plumb, time runs strangely. There are currents, the mad seers claim, that can sweep ships across the sea of time, and there are cities built to an alien geometry. [Which all means the elder gods can be both older and younger than the first one.]
In those cities dwell the elder gods, and their servants, chief among them their high priest Cthulhu and his star spawn. Now, those dread cities are rising from the depths, casting a shadow before them.
The telepaths are the first to sense it, their minds filling with visions of the elder gods, visions that leave even the strongest gibbering wrecks. A few, such as Spock and Bester, will eventually manage to pull themselves back to some semblance of sanity, though their eyes will ever be haunted, but most will never recover. Most had their minds utterly shredded in the first milliseconds of contact.
Knowing what is coming, the Shadows and the Vorlons abandon their plots and flee. With no one pulling the strings and the telepaths all mad, the B5 universe lurches to total war while paranoia runs rampant.
Next, the shadow of the elder gods, creatures that do not belong in any rational universe, warps the very structure of space and time, creating temporal anomalies and dimensional gateways, which is when the Enterprise enters the scene. [It's best if both the Enterpise and the villains arriving together is not a coincidence.]
Naturally, people will blame them for the problems, accusing them of being the scouts for an invasion. Resolving that allows for plenty more character scenes.
Then the slave races of the elder gods arrive, rising out of hyperspace to lay planets waste, starting with the weaklings who actually need ships, followed by wave after wave of stronger races, until come Cthulhu and his peers, any one of whom can destroy a planet bare-handed, and after them, the elder gods themselves. This allows for a lot of thrilling battle sequences.
Ideally, our heroes will stop the invasion before the elder gods arrive. Once they've worked out they're all on the same side, they'll need to work out what's going on, then venture into the depths of hyperspace themselves (for which, conveniently, the Enterprise happens to be well suited) and confront the elder gods in their eldritch city even as the final battles rage in the normal world, a thousand last stands.
Winning won't be easy, but if it was you wouldn't need heroes to do it. Great heroes need great challenges to show their mettle, which is why triumph over adversity is a classic tale. It's also why easy victories make for weaker stories.
You can tell the same basic story with many other villains, of course. Nor would it change much if they were invading from other dimensions rather than from some hidden recess of the B5/Trek universe.