Bulwark of Defense: A thought experiment

[Rater202]

Bulwark of Defense (Ex): When you reach 3rd level, an opponent that begins its turn in your threatened area treats all the squares that you threaten as difficult terrain. Your strict vigilance and active defensive maneuvers force your opponents to move with care.

A third-level class feature from the Knight Class in players handbook 2.

Nothing else from The class appealed to me as much as this when I first read it many moons ago.

The image of a knight who'd taken the time to become proficient with a spiked chain using their weapon to constantly trip up and stall their enemies entered my mind, but alas I was young and unable to formulate a proper build... Though I understand that spike-chain wilders specializing in trip attacks were popular once upon a time so probably something like that to stay on theme.

But a stray thought occurred to me not too long ago, and now I'm wondering... Was I thinking too small?

So, just for fun...

What's the biggest "threatened area" we can give to a typical adventurer?(by which I'm saying someone with a bipedal body shape of medium or small size. Maybe large)

Are there any classes or feats that give you additional advantages when your foes are stuck in difficult terrain?

[Paragon]

Well
The Half Ogre Template LA+1 gives you Large size = 10ft. reach
The Enlarge Person(spell)/Expand (power) increases size by one step = 15ft. reach
Spike Chain is 10ft. reach weapon and by Srd
Large or larger creatures using reach weapons can strike up to double their natural reach so you're looking at 30 ft. reach

[Saintheart]

An alternative from Dragon magazine is Ranged Threat, all squares within 20 feet are considered threatened when you're armed with a ranged weapon, ie holding a weapon with the Throwing quality.

[H_H_F_F]

More levels of psychic warrior would let you eventually increase your size by more than 1 category using expansion. Deformity (tall) or inhuman reach should increase reach as well.

[Piggy Knowles]

Four levels of drunken master would give you improved improvised weapons, which allows you to use improvised weapons that have reach according to their length. The example given was a ladder, but any reason why that has to be the limit? What about, say, a rope? That would get you some pretty insane reach.

[The Viscount]

Years ago for an Iron Chef (https://forums.giantitp.com/showthread.php?270196-Iron-Chef-Optimization-Challenge-In-the-Playground-XLII&p=14723588#post14723588)round I did a spin on this.

The build isn't pretty, especially with how the old table code looks. The absolutely ancient internet meme doesn't help. The upshot is take the following feats.

Aberration Blood (prerequisite)
Inhuman Reach (+5 feet)
Deepspawn (to airtight qualify for extended reach)
Extended reach (+5 feet)
Willing Deformity (prereq)
Deformity (Tall) (+5 feet)


Which is 20 feet naturally. As stated, a reach weapon doubles this to 40. My favorite to use is the Duom from Dragon Compendium, since it can attack adjacent enemies as well and is only martial. Unfortunately Deformity (Tall) doesn't stack with size increases. If you're feeling cheeky or have a permissive DM, select "flexible limbs" for aberration blood and use that to qualify for extended reach.
The build used Shadowblade's ability to extend reach by an additional 10 feet for one round at a time, but I really don't think it's worth the 9 levels of that Prc.

For another approach, if you don't want to use weapons, tack on a 2 level totemist dip to bind the Displacer Mantle for an additional 5 feet of reach with the tentacles you get. As an added benefit, you can use those to qualify for extended reach.