Kaylon

Basically everything is allowed as long as it doesn't come from external sources. Probably the most OP build for the ultimate is a Bloodmage who steals the most powerful/useful priest/druid/wizard spells using the Grimoire Imprint trick... The assassin is probably the most powerful class you can build using SoF trick, but he will have more difficulties to keep Vela alive.

Playing Steel Garrote is useless for your setup since the drain applies only to melee weapons. Personally I wouldn't bother with anything else than Ghost Heart because without a real tank some pets will die sooner or later and it will add more problems. I would replace the wizard with an ascendant because he has great buffs (Brilliant, Robust,...) for the party, CC and accuracy. You need the paladin for healing and buffs - I would suggest a Kind Wayfarer or a Bleak Walker instead.

For a PC without infinite invisibility is not worthwhile, for NPCs under AI even less. Applying Gouging/Arterial Strike to multiple targets does more damage overall than striking from stealth a few times.

At first you should spend your focus on Phantom Foes and Mind Blades, later replace Mind Blades with Pain Block (keep it up on the entire party) and finally add Borrowed Instinct and Ancestor's Memory. You start the fight with Borrowed Instinct and Phantom Foes, while Pain Block/Ancestor's Memory can be scripted and left on AI.

You should make a clear list with the exploits you don't want to see because there's no general consensus here... What about using Salvation of Time/Wall of Draining to extend powerful buffs forever or using infinite DOTs to kill enemies while staying out of sight?

Serafen has good melee stats and works well as a barbarian using cipher spells to support himself. Just make sure Seraphen has high shock AR and stays away from the party.

If there are no enemies to flank that condition is considered true. When you become invisible (or after killing the last enemy) you lose aggro and there are no more enemies (they become just hostiles with no target).

I tried it on a dummy with an animist.

I tried to apply the DoT after Enfeebled and it stays under 15s for me (with 30INT)...

Strange... I didn't see Wildstrike working with FF and dots last 15s at best in my game.

Yeah, it opens new options for berserkers/tacticians and might help a lot vs Hauani if it breaks the merge and isn't affected by RES.

Of course you can play it in melee too with the right gear/abilities, stay alive using Unbending and become invisible from time to time to get back your resources. You can also flank multiple melee enemies using Persistent Distraction + Guardian Stance and trigger brilliant even without being invisible. But you shouldn't expect to be as effective or risk free as the sniper version. Anyway, you can see more details here:

An assassin/tactician sniper can solo everything with ease and doesn't require heavy buffing or infinite dots to kill enemies. The big ooze is the only tricky boss, however there's a very reliable (and relatively fast) method to kill it using the Mechanical Marvel and a few Tornado scrolls. There's always the paladin/troubadour, but I suppose you already know it - he can also shorten a lot the Hauani fight using Tornado scrolls. Paladin/forbidden fist is also a good candidate but he will struggle much more against Hauani. Paladin/soul blade can probably solo everything too if you don't mind doing shoot and run against Dorudugan.

You should try SC Forbidden Fist with high resolve - he can solo everything rather easily from the beginning to the end.

Devoted/monk with Scordeo's Edge works pretty well - lots of crits, free attacks, CCs. You can always switch to Scordeo's + Tuotilo's when you need more defense. Once you get Unbending Trunk you can even wear a light armor because you will outheal the damage from the enemies.

Monk/soul blade can have very high defenses while dealing also incredible damage. Sun and Moon + Tuotilo's Palm + Left Hand of the Obscured coupled with high accuracy (Borrowed Instinct) and Swift Flurry/Heartbeat Drumming are devastating with Soul Annihilation. The double hits of Sun and Moon will trigger Swift Flurry/Heartbeat Drumming even multiple times in a row recharging your focus after each Soul Annihilation. You will also terrify your target causing often disengagement attacks for even more free hits.

Ghost heart/ascendant with Frostseeker is a very fun/versatile ranged build with solid ranged damage and casting abilities. However if you want to play just a caster then the potential of Frostseeker is a bit wasted...

Ascendant/helwalker is the best combo for a caster cipher. Chromoprismatic Staff with Instruments of Pain is the most efficient way to recharge your focus because you can benefit from Swift Flurry/Heartbeat Drumming/Turning Wheel while attacking from range.

A trickster/soulblade can gain focus pretty fast and you can stack multiple dots on enemies.

Priest/streetfighter combo has good synergies and the 30% lash on spiritual weapons is pretty good. Druid/Trickster using Firebrand can work too.

Maybe I was thinking about Frenzy and Swift Strikes and I assumed that Tactical Barrage is suppressed by Frenzy too. However they should stack indeed because the hit to crit from Frenzy applies only to melee weapons, while the one from Disciplined Strikes works with all attacks.

You can't do the same with Set to Their Purpose... ?

If I remember well it appears as suppressed in the active affects when you put your mouse over character's portrait during combat. I never really tested because it made sense to me...

Disciplined Strikes will be suppressed by Berserker Frenzy thus you should pick Tactical Barrage instead. With Barbaric Blow you will have 1-(1-0.3)*(1-0.3)=51% hit to crit chance. Here's the link @Not So Clever Hound mentioned earlier

Powder Burns distracts, doesn't confuse. A streetfighter/troubadour might be a better combo because Chillfogs benefit from sneak attack, deathblows and heating up bonuses.