Vanilla assassins are pretty boring and pose no real challenge. Vanilla behaviour is as follows:

Assassin (Level 6-45);
 - Races: (F) Khajiit, (F) Argonian, (M) Dark Elf
 - Weapons: Leveled Sword, Dagger
 - Perks: None
 - Armor: Worn Shrouded Armor, 25 armor
    // All in all very boring without any variety. They also scale very bad without any perks or any enhancements into the higher levels and pose no challenge whatsoever



This mod does the following to address this:

General Changes;
 - Races: (F) Khajiit, (F) Argonian, (M) Dark Elf, (M) Wood Elf, (F) Imperial, (M) Nord
 - Class: CombatThief -> CombatAssassin
    // Same as all Dark Brotherhood members, unsure why it was on CombatThief in the first place
 - Increased health and stamina offsets
 - 50% to spawn melee assassin, 50% to spawn ranged assassin
    // A unused ranged assassin template & missileAssassin combat style are still present in the game, this mod reintroduces them


Brotherhood Assassin (Melee) (Level 6-20);
 - Weapons: 2x Leveled Sword
 - Perks: None
 - Armor: Worn Shrouded Armor, 25 armor

Broterhood Assassin (Ranged) (Level 6-20);
 - Weapons: Leveled Bow (50%) or Crossbow (50%), Leveled Sword
 - Perks: None
 - Armor: Worn Shrouded Armor, 25 armor

    // The Brotherhood Assassin is essentially the same as the vanilla Assassin, with the exception of either dual-wielding 2 swords or spawning with a ranged weapon. As for why dual-wielding: It dishes out immense damage while offering little to no defensive capabilities. Seems fitting for an assassin who wants to end a fight as quickly as possible, hence why all melee assassins duel-wield. It also makes them a bit more unique so thats a plus in my book


Brotherhood Executioner (Melee) (Level 20-40);
 - Weapons: 2x Leveled Sword
 - Perks: Custom Fit, Fighting Stance, Devastating Blow, Bladesman, Dual Flurry, crExtraDamage02
 - Armor: Upgraded Worn Shrouded Armor, 58 armor

Brotherhood Executioner (Ranged) (Level 20-40);
 - Weapons: Leveled Bow (50%) or Crossbow (50%), Leveled Sword
 - Perks: Custom Fit, Fighting Stance, Power Shot, Critical Shot, crExtraDamage02
 - Armor: Upgraded Worn Shrouded Armor, 58 armor

    // The Brotherhood Executioner packs a stronger punch in every way, perks are on-par with bandit archers and their increased armor rating should help protect them a bit more


Brotherhood Silencer (Melee) (Level 40-Unlimited);
 - Weapons: Leveled Enchanted Sword, Leveled Sword
 - Perks: Custom Fit, Fighting Stance, Devastating Blow, Bladesman, Dual Flurry, Dual Savagery, crExtraDamage025
 - Armor: Upgraded Worn Shrouded Armor, 58 armor
 - Misc. Item: Enchanted Ring, One-Handed (Increases one-handed damage)

Brotherhood Silencer (Ranged) (Level 40-Unlimited);
 - Weapons: Leveled Enchanted Bow (50%) or Enchanted Crossbow (50%), Leveled Sword
 - Perks: Custom Fit, Fighting Stance, Power Shot, Critical Shot, Ranger, Bladesman, crExtraDamage025
 - Armor: Upgraded Worn Shrouded Armor, 58 armor
 - Misc. Item: Enchanted Ring, Marksman (Increases missile damage)

    // The Brotherhood Silencer will offer more of a challenge than your average bandit, perks ranks have increased across the board and the enchanted weapons will deal significantly more damage. They also wear enchanted rings dependant on their favoured weapon, increasing damage output even further. Their defense remains lacklustre but these guys plan to end fights sooner rather than later



Optional Faction Crossbows Patch;

Brotherhood Silencer (Ranged);
 - Weapons: Dark Brotherhood Crossbow, Leveled Sword
 - Ammunition: Dark Brotherhood Bolts (25%), Elemental Dark Brotherhood Bolts (75%)
    // Be aware that these guys might one-shot you when using difficulty-increasing mods. The DB Crossbow introduced by Faction Crossbows is one of the strongest ranged weapons found in the game



Thoughts on balancing & other related stuff;
I made sure to not increase their power levels to inappropriate levels but can't take every difficulty-increasing mod into account. Depending on the mods you have enabled that change the difficulty, for example KYE and wildcat, you might not have a good time when fighting these guys. The assassin encounter was always very lacklustre and the spawned assassin have been buffed in every way, please be aware that other mods can change the strength of these enemies

Ranged assassins were removed for probably this reason: They can be annoying. There's still an unused rangedAssassin template + a missileAssassin combat style so they most likely were ditched for that reason as I can't see any other since they seem to work fine in combat. Getting hit out of nowhere can be annoying but hey, we're Skyrim experts at this point and every bit of random new stuff happening is exciting (at least I think so), so I decided to reintroduce them. Have fun!

I'm not aware of ways to force a specific random encounter so I couldn't test this mod as much as I would've liked to. However, I've spawned every NPC and everyone worked fine - I also didn't change the encounter quest record, only the nested leveled list so there shouldn't be any problems on that front

If you want assassins to actually use poison against you, I fully recommend Smart NPC Potions: https://www.nexusmods.com/skyrimspecialedition/mods/40102?tab=description



Compatibility;
Technically not compatible with...
 - Mods that change the assassin leveled list
    // While this mod doesn't change the vanilla assassin at all to ensure compatibility, it does change the assassin leveled list which is called upon the assassin world encounter happening

This mod uses vanilla leveled weapon lists. Mods that change these, for example MLU and WACCF, are therefore also changing the weapons assassins can spawn with



Credits (don't forget to endorse these!);
 - https://www.nexusmods.com/skyrimspecialedition/mods/164, the xEdit team for creating SSEEdit
 - https://www.nexusmods.com/skyrimspecialedition/mods/4047, Deserter X for the wonderful mod 'DX Faction Crossbows'