Though They Be Great (Giant Foe Procedure)

I was never really satisfied with mechanics for fighting really big guys. Vaulting up to a cyclops's eye or clambering along a dragon's scales to stab at its heart should probably be resolved differently than a series of grapple or attack rolls, but it shouldn't be crazy complicated, but but but it shouldn't blindside me when I forget to prepare and the players want to start scaling my hydra but but but it should feel like a risky maneuver that walks the line between being a default strategy and suicidal gambit.

Here is what I'm thinking.

If a monster is 20+ feet tall or long (6 meters toff or blimey for metric readers), we'll call it a giant and you MAY scale it. If a monster is 50+ feet you MUST scale it to damage it in melee.

Rather than giving giants a lot of HP, give them DR-- 2 for the most minor giants, 4+ for proper giants. This assumes that your game has variable weapon damage, and thus having 4 DR means daggers are all but useless against a creature that dwarfs them.

Each particular giant will have different traits. I'm assuming you will assess penalties and bonuses based on common sense. Difficulty or ease of scaling, which attacks can target someone on them, unique affordances, and so on.

Anyone next to a giant can take a turn to scale them. They can get to any part of the giant with a 3-in-6 chance, modified by dexterity modifier (or on a dex save or however you want it to work.) on a failed roll, they fail to make progress-- they can either release and fall down to the ground or just hold tight and wait until next turn.

Like humans, every giant has weak points-- joints, nerves, eyes, whatever. You don't need to list them out, but giving a giant a special weak point with a custom ability is cool. Attacking a weak point is the main goal of climbing a giant, because up close your attack against a weak point ignores the giant's DR. Ranged attacks are assumed to be targeting weak points by default, but only line up a perfect, DR-shrinking hit on a critical hit.

Giants can attack those who are scaling them (as long as this makes sense) but they can't divide their attention between scalers and other enemies. Or, instead of attacking, they can try to delope anyone scaling them-- rolling around, brushing and batting, rubbing against a cliff face, exc.  If they do so, anyone scaling them has to make an immediate climbing roll or fall off.

And that is the procedure. Simple, to give a good wide base to all variations and tactical infinities. The risk of losing a turn is hopefully big enough to make the endeavor feel like taking a chance.

Some simple examples:

Minor Giant: HD 6, AC 14, pole-axe +4 (1d6 in a 20' line) OR grab +4 (1d6 and grapple).

DR 2. Protruding and crude armor gives +1 to climb.

Weak points: armor joints, visor holes, beard.

Can't attack scaling enemies with pole-axe.

Ash Dragon: HD 8, AC 12, claw x2 +6 (1d6) AND bite +6 (1d6 and grapple) OR breath (3d6 in a cone, save for half).

DR 4. Dusty serpentine body gives -1 to climb rolls when it's trying to delope you.

Weak points: heart, underbelly, mouth. If it fails to bite or you grapple your way out of its mouth, you can hold onto its teeth for free, giving immediate access to its weak points mouth but giving -2 AC vs its bites and -2 save vs its breath.

Malasaurus: HD 4, AC 10, trample (save or take 1d6 and fall prone) OR thagomizer +4 (1d6 in 90 degree sweep or 2d6 direct slam) AND beak impale +8 (1d6 but sticks head to ground until pried out)

DR 8. Clumsiness and clumps of feathers give +2 to climbing rolls. 60 feet tall at the shoulders and 120 at the top of the head, therefore must be scaled to harm in melee

Weak points: base of neck and tail, head (which can be attacked without scaling when it's stuck in the ground).

Can't trample or impale scaling enemies, but can thagomize scalers and attack other foes due to a simple second brain in the base of the tail.

A Conspiracy of Ravens on the glog server has some foe-climbing rules in their Carrion Gods RPG you could compare to.