Edit: I forgot to add my reasoning as to "why" I think they should have set effects. The reason why is because most of them just seem underwhelming. the Snarbo and Demo Suit are pretty nice already but the others either have too little of an effect (compared to other normal sets) or they have no effect at all. Having them do something cool for equipping both would encourage people to get them and actually use them for more than just a costume over their Black Kat/Chaos sets.
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★ Snarbolax Set ★
Set Bonus A
- Melee attacks have a chance to poison enemies.
- Enemies that you poison are slowed for the duration of the poison. (50% slow PvE, 20% slow PvP)
Set Bonus B
- Melee attacks have a chance to poison enemies.
- Damage bonus vs poisoned enemies: Medium
Rabid Snarbolax is poisonous so the theme for these set bonuses is using melee (or other poisonous weapons/items) to inflict your enemies with poison and get a neat buff. Bonus A focuses on making poisoned enemies easier to manage while Bonus B just focuses on more damage. Medium(Helm) + Medium(Armor) + Medium(Set) = Maximum
Note: Snarbolax is arguably one of the strongest (and most used) SL sets so it doesn't really need a buff, but I figured I'd include it since I was doing the other less used sets.
★ Mercurial Demo Set ★
Set Bonus A
- Killing an enemy in the Construct family causes them to explode and deal damage to nearby enemies.
- Damage bonus vs constructs: Medium
Set Bonus B
- ??? Possibly something related to shock/being shocked.
- ???
It's a bomber suit. It has to make things explode. Adding the construct damage makes it a bit more specialized in PvE. The explosion effect would be really nice for construct themed arenas.
★ Almirian Crusader Set ★
Set Bonus A
- Curses you inflict on enemies are also applied to other nearby enemies.
- Damage Bonus vs Cursed enemies: High
Set Bonus B
- Whenever you kill a cursed enemy their curse is applied to nearby enemies.
- Damage Bonus vs Cursed enemies: High
Set Bonus C
- Burning damage is reduced to only one health pip.
- Your burns last 4 seconds longer.
- Damage bonus while burning: Very High
The idea for Bonuses A and B are the same (but with different methods to spread the curse). One concern I have though is the only way to really apply curse effectively is by using Gran Faust (or curse vials). Bonus C is sort of a "fun" bonus that takes the set's negative fire resistance and turns it into more of a positive for you.
★ Ice Queen Set ★
Set Bonus A
- The player is covered in an icy aura while shield bashing. (Freezes enemies you hit with the charge.)
- Damage bonus vs frozen enemies: Maximum
Set Bonus B
- Shielding causes the player to release an icy wave around them at the cost of 15% shield health.
- Damage bonus vs frozen enemies: Maximum
Set Bonus C
- Shielding causes the player to emit a freezing vapor around themself. (Causes shield health to drain while shielding.)
- Damage bonus vs frozen enemies: Maximum
These are pretty much all the same effect but the way you apply the freeze is different with each one. The idea for is you freeze your enemies (by using your shield health as a resource) and then you hit them out of the freeze with any weapon you desire for a big damage bonus.
★ Arcane Salamander Suit ★
Set Bonus A
- Killing a slime or beast causes the player to camouflage for 3 seconds. (Attacking in camouflage makes you visible.)
- Damage bonus while after exiting camouflage: Medium (2 seconds)
Set Bonus B
- ??? Possibly something related to consumables.
- ???
Bonus A is possibly too powerful on levels that are only inhabited by beasts/slimes. If you kill quickly enough you could just have 100% uptime on it and you'd never take damage...
★ Heavenly Iron Set ★
I have no idea how to make an effect themed around this set... Maybe something like "using health capsules or picking up hearts shares them with nearby party members" or something would fit the "heavenly" aspect of it but anything related to party healing would probably be too broken.
Set bonuses can be interesting, however honestly simply buffing shadow lair gear would prove better. The issue with some shadow lair gear isn't their stats, but rather that there are other things better than them - most of the sets are balanced pretty well for what they're crafted from. Here's a quick rundown:
Almirian set gets an abnormal amount of normal damage resistance. The shadow resist is nice, but it's a sidegrade to cobalt, which already isn't that great. The fire vulnerability should be scrapped, however, since curse is such a rare status anyways.
Arcane Salamander gives very high normal and elemental resistances, rivaling that of specialist defender sets (divine set, dragon scale). The damage bonuses on it don't make much sense, but the defense it provides is great.
Heavenly Iron exchanges fire weakness out for shock, and its poison resistance out for increased normal defense. The fiend damage bonus is split into fiend and sword lows.
Ice Queen is literally just Royal Jelly but with freeze resist instead of sleep. Not a bad set, but not the most helpful either.
Mercurial Demo is great where it stands. It exchanges damage for MSI and snags some great shock resistance.
Snarbolax is great too. It's skolver but it exchanges piercing defense for shadow defense, and one point of freeze resist for 3 points of poison resist.
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Granted, you likely knew a lot of this, which is why you made your suggestion. Still, it's important to note how shadow lair sets are sidegrades rather than upgrades. If the set was already good the shadow lair version is great. If the set isn't too good the shadow lair set isn't the best, but it isn't too bad either. I want to say that's by design.
If we were to add anything else to these sets, a small boost of something would be neat. For example, Heavenly Iron could have sword MSI: low, meaning they would move slightly faster holding swords. Ice Queen could have bomb CTR: low, making it essentially a piercing bomber set (finally!) and not some strange skolver jelly hybrid. Arcane salamander could have +2 to some status (poison, shock). Almirian crusader could have no fire vulnerability plus sword CTR: medium per piece. Mercurial Demo and Snarbolax are already pretty decked out with stats, so they could be left untouched.
Basically, if we can specialize the shadow lair sets while still making them sidegrades, that's better than straight up making them the only choice. Filling in some gaps in our arsenal (pierce bomber, sword CTR) would also provide some incentive to go after these sets that have unique bonuses, despite them potentially being outshined by other sets.