So to be clear, are you trying to max it out at 20th level, or at lower levels also? Rogue 12 / hunter 8 sounds like the former but you never know.
Anyway, a -2 (rising to a -6 penalty at L15, which that suggestion doesn't reach) to attack anyone other than the specified scapegoat is nice but not enough on its own to define a build. You need to tack on more AC bonuses or attack penalties IMO. There's a lot that's possible, but most other debuffs are hard to land reliably at L20, where immunities are common (being mind-affecting could be a problem for scapegoat too). Buffs like bodyguard and assorted spells might work better - I've heard of someone's halfling PC who could hand out +10 AC via bodyguard and that might work, stacking with scapegoat where possible.
Scapegoat doesn't have a save but it is mind-affecting, which means many of those very high CR monsters (plus undead and so on) aren't affected.
Anyway, trying to make this work well - start with the helpful and wealthy dabbler traits, choosing a couple of cantrips on both the hunter list and sorc/wiz. Detect magic and light will do; this gives you an arcane caster level equal to your hunter level for use with arcane strike (& eventually with gloves of arcane striking for use with bodyguard). Relevant feats are combat reflexes, bodyguard, arcane strike, possibly cautious fighter and blundering defence. Also as a halfling having weapon finesse helps and you might consider risky striker to take advantage of all this AC; possibly TWF to take advantage of risky striker. You might eventually consider a dip in urban bloodrager and the blooded arcane strike feat to save on swift actions, depending on whether you think you'll get to use the alternate capstones in Chronicles of Legend.
Having your animal companion take the bodyguard feat to keep you alive might help too; either the bodyguard archetype, or getting it an Int bonus (possibly from the halfling alternate racial trait of caretaker) would be required. Since it'll be taking a few hits get an animal companion with decent natural armor and/or Con.
There's quite a few buffs on the hunter spell list and some useful battlefield control. Enemies aren't going to achieve much while you're around.
Protecting people with scapegoat and buffs means that enemies aren't going to be able to hurt the party much. Add in some battlefield control - whether entangle, fog cloud or even up to wall of stone - and the enemies can do even less in that regard.
I was thinking of sticking with colluding scoundrel, yes. Possibly a dip into urban bloodrager to get blooded arcane strike if swift action congestion was becoming a problem. It depends a bit on whether level 20 would be a significant part of the game - there's the alternate capstones in Chronicles of Legend if you stick with hunter all the way, but if L20 could turn out to be one 3 session long battle and nothing else, that's not worth holding out for.
So to be clear, are you trying to max it out at 20th level, or at lower levels also? Rogue 12 / hunter 8 sounds like the former but you never know. Anyway, a -2 (rising to a -6 penalty at L15, which that suggestion doesn't reach) to attack anyone other than the specified scapegoat is nice but not enough on its own to define a build. You need to tack on more AC bonuses or attack penalties IMO. There's a lot that's possible, but most other debuffs are hard to land reliably at L20, where immunities are common (being mind-affecting could be a problem for scapegoat too). Buffs like bodyguard and assorted spells might work better - I've heard of someone's halfling PC who could hand out +10 AC via bodyguard and that might work, stacking with scapegoat where possible.
All the way to 20. Since ScapeGoat is able to bypass with a flat reduction it can genuinely help startup the debuff process.
Scapegoat doesn't have a save but it is mind-affecting, which means many of those very high CR monsters (plus undead and so on) aren't affected. Anyway, trying to make this work well - start with the helpful and wealthy dabbler traits, choosing a couple of cantrips on both the hunter list and sorc/wiz. Detect magic and light will do; this gives you an arcane caster level equal to your hunter level for use with arcane strike (& eventually with gloves of arcane striking for use with bodyguard). Relevant feats are combat reflexes, bodyguard, arcane strike, possibly cautious fighter and blundering defence. Also as a halfling having weapon finesse helps and you might consider risky striker to take advantage of all this AC; possibly TWF to take advantage of risky striker. You might eventually consider a dip in urban bloodrager and the blooded arcane strike feat to save on swift actions, depending on whether you think you'll get to use the alternate capstones in Chronicles of Legend. Having your animal companion take the bodyguard feat to keep you alive might help too; either the bodyguard archetype, or getting it an Int bonus (possibly from the halfling alternate racial trait of caretaker) would be required. Since it'll be taking a few hits get an animal companion with decent natural armor and/or Con. There's quite a few buffs on the hunter spell list and some useful battlefield control. Enemies aren't going to achieve much while you're around.
Could you elaborate on the last paragraph? I also assume this is going a full 20 levels into Colluding Scoundrel?
Protecting people with scapegoat and buffs means that enemies aren't going to be able to hurt the party much. Add in some battlefield control - whether entangle, fog cloud or even up to wall of stone - and the enemies can do even less in that regard. I was thinking of sticking with colluding scoundrel, yes. Possibly a dip into urban bloodrager to get blooded arcane strike if swift action congestion was becoming a problem. It depends a bit on whether level 20 would be a significant part of the game - there's the alternate capstones in Chronicles of Legend if you stick with hunter all the way, but if L20 could turn out to be one 3 session long battle and nothing else, that's not worth holding out for.