Armies, guards for shadows, golems - all hit a pretty solid barrier in Amber: Combat Mastery, Deadly Damage, Endless Stamina. Such defences are no match for even a weak Amberite. However, we know that Amberites can be taken down if sufficiently outnumbered, either by an eventual case of bad luck for Bleys, or simply swarming Corwin from all sides.
So the way to make swarming easier, is to make the creatures smaller. Rather than surrounding an Amberite with 6 humans, Pratchett's Nac Mac Feegle might provide a hundred of so simultaneous attackers; winged pixies armed with razors several hundred; enhanced wasps a couple of thousand; self-mobile grains of sand tens of thousands....where does the race end?
Well, for magical shadows, at the atomic level: "a-tom" is literally "not-cut" ie indivisible. So a plan to swarm an opponent with a neutron for every atom in his body may work in a high tech shadow, but would likely fail elsewhere. Similarly alchemical attacks will fail outside of magical shadows.
However, light is available nearly everywhere. Weaponizing photons has a number of interesting side effects:
- sunlight destroying vampires etc would be a reflection of the reality where light is taking out any opponent, plus the opponents being vampiric invaders.
- the light would slow down: from a game mechanic perspective because Engine Speed is the practical limit of enchantment, from a scientific perspective because of the extra mass added by the enchantments. So the 'sunrise flowing over the hills' of Discworld would also become a thing.
- the limited effectiveness of beam weapons in space operas becomes understandable; the light beams are used not because they are deadlier than bullets (they're not) but because being shot by one beam weapon is the equivalent of several hours of rifle fire, it just cuts down the time required to get to that 'lucky shot'.
These weapons could actually make Endurance useful - sure, you have the warfare to avoid being damaged by the first few hundred photons, but only Endurance will let you repel a hundred hours of attacks...every second.
Those with access to Demonic assistance can up the damage levels somewhat, creating Destructive weapons - possibly beams of 'dark energy' or something similar: and other shadows will have reflections of this, frex the Taint in L5R.
Of course, defences call also be miniaturized, creating defence in depth. Eventually, that will result in sci-fi type 'shields' - and explain why a force field that stops light weapons can be seen through: it stops the enchanted upgrades rather than the light itself.
Finally, Implants can be designed to protect each individual cell in the owner. This would be particularly appreciated by Shapeshifters: while the defences would be useless against a Pattern weapon, the resulting flames would immediately smother, unable to spread.