You're so big that you count as more than one combatant! For each level in this Ability, you have a secondary Component that can act as another character in a fight. Your Components' Abilities (and Weaknesses) are identical to your character's, but they can have extra Abilities (and Weaknesses) totaling up to your level in Component. While each of your Components has its own pool of 10 base Health and its own attacks and defenses, they share your initiative and Endurance. When a Component’s Health is depleted, it is destroyed (or otherwise disabled) and its Abilities and attacks can no longer be used. However, your Components' Heath totals aren't vital to you -- if your core Health and Endurance are reduced to zero, you're still defeated, even if your Components are otherwise healthy!
(My intent was originally to call it Gestalt, as suggested, but other OVA Abilities that give characters things -- Companion, Gear, Minions, Endurance Reserve, etc -- are named after those things, so Abilities don't introduce additional terminology, and I thought that would be a good example to follow.)
------------------ Original Post ------------------
A number of my players are Monster Hunter fans and I like running those kinds of monsters, so we end up with a lot of called shots aiming at specific parts of monsters. Additionally, this is the way I ran extra attacks for those monsters before Extra Actions became an official boss feature in Revised. It's also a little bit similar to how big D&D monsters are run, with specific attacks per turn. (Er. Last time I checked, anyway. I'm actually only familiar with like super old D&D rules, heh.) So to that end, here's a new Ability!
New Ability: Multipart
- For each level of Multipart, the monster has a secondary part which can act and be acted on separately. These parts have 10 Health and may have an Ability total of up to the monster's level in Multipart.
- A monster’s parts share the monster’s core Abilities and Weaknesses. A monster's parts can have increased or decreased levels of those Abilities (similar to Gear or Transformation.)
- Each of a monster’s parts has its own pool of health, attacks, and defenses, but shares the monster’s initiative and Endurance.
- When a part’s Health is depleted, that part is destroyed or disabled and its Abilities and attacks can no longer be used.
Greater Wyvern (Boss) TV: 38 (14+11+13)
- [40/40] [Defense Roll: 1] [Armor: 3] [Initiative: 1]
Attack +3, Armored +3, Strong +2, Agile +2, Resistance: Fire +3, Multipart +2, Awkward Size -2, Slow -1, Vulnerability: Ice -1, Vulnerability: Water -2
- Chomp! [Roll: 4] [DX: 6]
The wyvern snaps at one of its enemies with its sharp teeth.
- Fireball [Roll: 4] [DX: 4] [End: 10] Area Effect, Continued Effect, Ranged, Delayed, Unwieldy
The wyvern takes a deep breath, then hurls a fireball at a group of enemies. Affinity: Fire
- Furious Charge [Roll: 4] [DX: 10] [End: 10] Area Effect x2, Effective x4, Stunning, Assisted (Wings), Open to Attack
The wyvern smashes its whole body through a group of enemies.
-  [Defense Roll: 3] [Armor: 1]
Flight +4, Evasive +2, Armored -2, Weak -2
- Talon Swipe [Roll: 4] [DX: 4]
The wyvern takes a swipe at an enemy with one of its wing talons.
- Aerial Prowess [Roll: 8] [End: 5] Defensive x5, Cancel: Indoors (-5), No Damage
The wyvern flies into the air, making it much more difficult to hit. (Note: Because this "attack" does no damage and its only effect works even if it misses, there is no need to roll. However, if a roll is necessary for some reason, the wyvern adds its Flight level to its roll.)
- Buffeting Wind [Roll: 4] Area Effect, Stunning, No Damage
The wyvern uses its wings to blow over its enemies. Affinity: Air
-  [Defense Roll: 1] [Armor: 3]
Agile +2, Tough +1, Weak -1
- Tail Bash [Roll: 6] [DX: 5]
The wyvern lashes its tail at an enemy.
- Flail [Roll: 6] [DX: 2] [End: 5] Area Effect x2, Ineffective x3
The wyvern flails its tail about wildly.
- Poison Sting [Roll: 7] [DX 4] [End: 5] Accurate, Continued Effect, Ineffective x2
The wyvern jabs an enemy with the poisonous barb on its tail. Affinity: Poison
- Because a monster and its parts are connected, they are always considered to be adjacent -- so an attack with the Area Effect Perk can affect multiple parts simultaneously.
- If a part needs its own Endurance pool, it can be given the Endurance Reserve Ability.
- If a monster gets any bonuses or penalties to rolls, those penalties apply to all the monster's parts -- unless it has the Self-Only Flaw, perhaps?
- A monster with the Multipart ability can make use of the Assisted Flaw for devastating attacks. But of course, the assisting part will still lose its action, and can't assist if it's been destroyed.
This might also be useful for giant mecha or spaceships or other such things, but it's inherently geared toward being an enemy ability. I essentially hacked together the parts I needed from Minions and Gear. It might need balance tweaks to make it usable for players. Maybe each level of Multipart should take 10 off the character's max Health? Adding levels of Tough (not to mention Health Reserves) isn't a problem for Bosses but might be a balancing factor for player characters?
A better name might be Composite? Primary and secondary parts need formal names, as well. I have typed the word "part" so much that it has ceased to be a word.
Just typing this up here has forced me to look it over and streamline it some more, so already this has been useful~
Thanks for any feedback!