"Never underestimate the power of a pretty face." —Common Wisdom
The Arena Champion Paragon Path has a largely overlooked, but highly optimizable level 16 feature.
Seize Opening (16th level): Whenever you successfully use Bluff to gain combat advantage in combat, you can make a basic attack against that target as a free action.
At a glance, this is basically useless, letting you make a basic attack with CA once per encounter after spending a standard action. However, the wording doesn't require you to actually use the feint action as defined under the Bluff skill's entry, but rather applies to any use of Bluff that gives you CA. This build accumulates a sufficient number of extra and off-action methods of using Bluff to gain combat advantage that it can make a free basic virtually every round.
This build's namesake is the Fire Emblem character Heather, a Rogue and serial con artist. The trick most naturally fits the Rogue, and as it's one of the few ways to gain a bunch of extra RBAs, I'll be using a ranged Rogue here. Most of the components are also accessible to other classes however, and it can be easily adapted for the Skald, Ranger, Blackguard, Warlock, Hybrid Executioner, and so forth. All you really need is a good Bluff check and a valid basic.
More checks means more rounds with more attacks. That part's simple. But which ones to use?
There are a number of ways to make off-action CA-granting bluff checks, not all of which are equally useful, not all of which are equally available, and some of which may raise eyebrows from your DM. I'll group the options by legal questionability, then goodness.
No iffiness here, they do exactly what it says: you make a bluff check, you get combat advantage.
Changeling Trick - Minor action duplication of the feint rule, meaning that your racial power now gives you a basic attack. Very hard to pass up.
Daring Performer - This feat gives the Rogue at-will Deft Strike a built-in feint. That by itself wouldn't be so amazing, except that this is an arena training feat, and therefore also satisfies a prerequisite for Arena Champion.
Astonishing Wound - One of the three reasons to use the Escaped Slave theme, this E7/17 can be used in melee or at range, has a bluff check for CA baked right in, and immobilizes the target on a hit.
Greenspawn Banespeak - This familiar gives a +2 bonus to bluff checks, and lets you make a bluff check as a minor action once per encounter. It requires you be arcane, which may not be worth the MC for Rogues, but Skalds and those who MC Skald are well-advised to take it.
Black-Hearted Knave - This theme's level 10 feature lets you use the feint action as a minor action. Redundant to Daring Performer for Rogues, but other classes may appreciate it, especially if they already have better encounter powers than Astonishing Wound.
These methods of getting CA via bluff check are more indirect, but still qualify.
Hidden Strike - When it works, this power makes creatures treat you as invisible, and therefore grant you CA. The second of the three reasons to be an Escaped Slave.
Dirty Tricks - Making a bluff check as a minor action to move one square without provoking gets you CA if you use it to move into flank.
Black-Hearted Knave - This theme's level 10 feature also lets you make a bluff check to create a distraction to hide, which will get you CA if it works, but requires you have good Bluff and Stealth.
Cutthroat - As with Black-Hearted Knave, this lets you create a distraction to hide as a minor action, and gives you Stealth training as well. It eats your MC slot though.
These don't legally work. Though you could try to put them past your DM anyway, I suppose. Cheater.
Perfect Feint - Minor action to gain CA with no check. This Rogue U6 requires Bluff to take, but doesn't actually use it in the power. If you somehow can convince your DM and guilty conscience that it's OK, it acts as a better equivalent to Dirty Tricks.
Battle Feint - This power gives an adjacent ally CA, not you. In order for it to count, your ally would need a rule of the form "any creature granting combat advantage to you grants combat advantage to your allies", and even that wouldn't work because it only gives them CA during their next attack, not for a time span. Dirty Tricks works in most of the same situations that this would though, so it's no big loss.
In addition to the rule elements that grant extra bluff checks that can be turned into attacks, there are a few other Bluff-check augmenting elements that deserve mention.
Note that the verbage on most of these rule elements is stricter than that on Seize Opening, which means they only apply to the "Straightforwardly legal" category above, but that can easily be 3+ times per encounter, and thus well worth taking.
Sambrese Rake - This feat gives an untyped +3 bonus and rerolls to your bluff checks made to gain CA and lets you shift 1 square whenever you make such a check. Requires Windrise Ports background.
Skilled Feint - This feat gives a smaller untyped bonus that only applies to the feint action, but it gives an extra die of sneak attack damage that lasts until the end of your next turn whenever you make a Bluff check to gain CA. Requires you be a Rogue, obviously.
Escaped Slave - Yes, there's more! In addition to its powers which were mentioned above, the Escaped Slave theme also gives you free skill training in Bluff.
Distracting Feint - This feat makes enemies who you make Bluff checks for CA against also grant CA to your allies. Could do worse.
Feign Injury - This feat lets you slide the target of a Bluff check to gain CA 1 square when successful, but only if you are bloodied at the time. Too situational, though it'd have been nice back when Spark Slippers were a thing.
Deception Mastery - This feat lets you use Bluff for deception rituals, gives a +2 feat bonus to bluff, and allows you to eschew the component cost of a deception ritual once per day. Totally campaign-dependent in utility.
With the exception of working in the above stuff, the choices made are pretty standard. It's a tough choice between Skald and Seeker for the MC here, but this build goes with Seeker because more RBA damage is always nice.
Note that Precision Throw allows the replacement of Brutal Scoundrel's STR damage with DEX, assuming you apply your SA on an RBA.
Class: Rogue, Rogue Weapon Talent, Brutal Scoundrel
Theme: Escaped Slave
Paragon Path: Arena Champion
Background: Entertainer, Windrise Ports (+2 Bluff)
Stat line: 10/11/18+2/12/13+2 initial, 11/12/24/13/19 present
Feat 1: Precision Throw
Feat 2: Light Blade Expertise
Feat 4: Silvery Glow
Feat 6: Superior Will
Feat 8: Primal Sharpshooter (retrained into in paragon)
Feat 10: Daring Performer
Feat 11: Lasting Frost
Feat 12: Nimble Blade
Feat 14: Primal Eye
Feat 16: Sambrese Rake
At-will Attack Powers:
At-will 1: Deft Strike
At-will 1: Acrobatic Strike
Encounter Attack Powers:
Encounter 3: Darting Strike
Encounter 7: Snap Shot
Encounter 11: Taxing Strike
Encounter 13: Astonishing Wound
Daily Attack Powers:
Daily 5: Bloodbath
Daily 9: Knockout
Daily 15: Rogue's Recovery
Racial Utility: Changeling Disguise
Racial Utility: Changeling Trick
Theme Utility: Hidden Strike
Utility 2: Sneak in the Attack
Utility 6: Dirty Tricks
Utility 10: Swift Parry
Utility 12: Hidden Reserves
Utility 16: Leaping Dodge
Torc of Power Preservation +3
Shadowdance Armor +3
Frost Dagger +4
Dagger of Speed +2 (RARE)
Bracers of the Perfect Shot (Paragon)
Siberys Shard of Merciless Cold (Paragon)
Gloves of Ice (Paragon)
Eagle Eye Goggles (Heroic)
At level 16, when the build's trick comes online, you have 5 ways to trigger bluff checks (2 minor actions, 2 baked into standard action attacks, 1 free) and additional minor action attacks from Swift Shot and Weapon of Speed. Add in Darting Strike and you net 13 attacks in five rounds without AP expenditure or outside assistance, with five (no AP, must move) to seven (AP, convert move to attack) attacks in your nova round.
Bluff modifier: +8 half-level, +5 trained, +4 CHA, +2 racial, +2 background, +3 Sambrese Rake for a total of 1d20+23 with the ability to reroll once. The hardest creature to trick that I was able to find in the MM that you might fight at this level was a level 20 elite who had passive insight of 32, which you still have a 76% chance of beating. Adding an item bonus to bluff might be useful, ideally Ioun's Revelation (level 3 alternative reward) or the Eye of Deception.
RBA attack modifier: +8 half-level +7 DEX +4 enh +3 prof +2 expertise +2 CA +1 Rogue Weapon Talent +1 nimble blade +1 item for a total of 1d20+29 vs. AC. Expect to never miss with RBAs.
RBA damage modifier: 1d4 +3d6 +7 DEX +7 DEX +7 DEX +5 vuln +4 enh +4 item +3 feat +3 shard +2 light blade expertise +2 gloves for a total of 57 average damage on a hit. (40.5 without Sneak Attack)
Non-RBA damage modifier: +7 DEX +5 vuln +4 enh +3 feat +3 shard +2 light blade expertise +2 gloves, for a total of Xd4+26. Yeah, the lack of +item to these bites, but there's not much to do about it, at least until you get the Ioun Stone of Agility in a couple levels.
This means your lumped damage on a non-nova turn should be roughly 85, or 55% SMHP. Not Kulkor, but not bad.