OSR Boss Fights: A Simple Recipe

From time to time I tinker with a ruleset that is an abominable crossbreed of OSR concepts and the Heroic Fantasy aimed at by 5e. This ruleset may never see the light of day, but here's a little portion of it, inspired by Skerples and various others. 

Boss Fights

A Boss is a unique creature that is designed to be dangerous for a full party of 3-5 adventurers of average level equal to its HD. Boss creatures are marked in the creature section with an *.

A boss’s HP is equal to its HD*10.

Boss Actions:

A boss activates 3 times per combat round: once during its normal turn, once at the end of the combat round, and once as a telegraphed action. A telegraphed action is announced at the start of any player’s turn, and then occurs immediately following that player’s turn.

Boss Saves:

If a boss fails a saving throw it may choose to only partially suffer the negative effects. E.G. it may be polymorphed into a half-dragon, half-rabbit abomination. Or a knight targeted by the sleep spell may fall asleep at the end of the next round as he fights the spell with all his will. A boss may only do this once per combat.

Boss Abilities:

Beyond additional HP and actions, a boss may have additional capabilities, such as the following:

• Damage Reduction
• Damage Immunity
• Area of Effect Attacks
• Damaging Aura
• Status Infliction
• Unique Mobility (Fly, Swim, Tunnel)
• Gains an additional Telegraphed attack on low HP.

Weaknesses:

A boss can also have 1-2 weaknesses. These are often well-guarded, perhaps requiring a specific kind of attack (such as fire), or simply having a higher AC. A weakness may inflict double damage on the boss, remove or delay an ability after taking a certain amount of damage, or have some other effect. Players may learn about a boss’s weakness by carefully observing the boss, or by studying before encountering the boss.

A Sample Boss: The Assassin in Red

A killer robed in red, wielding dual blades. An acolyte of an assassin’s guild, often hired to kill important individuals or troublesome groups.

HD: 1* (10 HP)

AC: 16, Light & Mobile

ATK: Dual Blades (+1, 2d6, keeping Highest, Fray Dice: d4 A fray dice is rolled with each attack, and may either be added to the To-Hit roll, or the damage roll. If a fray dice rolls a 4+, the fighter may attempt a maneuver in addition to the attack.)

MOR: 9

NARROW DODGE: While not held in position by anything, reduces all damage taken by 2.

SWIFT: Gains advantage on saving throws against dodgeable dangers. The Initiative DC against this boss is 14.

DEFLECTION: Knows the spell Deflection, and has 1 MD with which to cast it.

DASH ATTACK: Telegraphed, Faces a target within 45’, braces for a leap. Launches at the target, then attacks with advantage.

UNSEEN: The assassin has the thief’s Hide and Sneak talent. (It typically just succeeds at these tasks, rather than requiring a roll. If a roll is deemed necessary anyway, it rolls 3d6 and takes the highest).