You can run gauntlets by earning tickets. Tickets drop from hard mode bosses (sadly, they do not drop from hero mode bosses). The holder of the ticket must launch the boat. Everyone can join for no token cost, and the run costs no gear durability. Each gauntlet can be run 3 times, so you could theoretically run 12 gauntlets a day between boats 1-4. The ticket is consumed upon launching the boat - no refunds.
Several bosses will spawn with random modifiers attached to their name, changing various attributes like attack speed, AI behavior, additional attack effects, etc. See list at bottom for fill details.
The final boss has an openable sack in its loot table, and you may obtain no sack or several of them. Inside is always gold, sometimes AP capsules, and very rarely the gauntlet title. Sometimes the "final" boss will show up before the other bosses are dead (Black Breeze, Polar Bear, etc.) but the gauntlet isn't cleared until all bosses are dead. Playing on Hard mode gives you an extra drop from the gauntlet boss, which is an extra chance at a sack. Bosses can spawn with a variety of modifiers.
Most bosses have increased stun resistance. This has the side effect of making Fionas even less useful than they usually are.
Like in Hero Mode, SP is granted to all party members when an enemy is killed.
Always kill the most dangerous enemy first. This ensures you don't end up with a dangerous enemy replacing a weaker one, leaving you with two dangerous enemies.
One of the less reputable tricks is called assist spamming where one person repeatedly assists then leaves, bringing a new set of secondary weapons and feathers each time. This can be repeated indefinitely. This is a gray area that could very well be considered an "exploit" by Nexon. Use with caution.
As you might expect, scythe Evies are the most useful in the gauntlet. Golems, wisps, gravity inversion, free rezzes, free magic shield hits, blink, etc. all make them extremely valuable for surviving mistakes, distracting the enemy, recovering from deaths, and stunning bosses. Scythes continue to be the most OP weapon in Vindictus. It's extra unfair to Fiona with enemies that she can't even block.
Perilous Ruins Gauntlet
The most dangerous spawns are gnoll chieftains and werewolves. If those two don't spawn, you're in for a very easy run. I've cleared this gauntlet in 6 minutes when we got a string of easy boses. If you're in the Chieftain area, lure black breeze to the large pillars so he has less room to bounce around in. It's very easy to trap him by the pillars with a golem, mercury, chain hooks, etc, at which point you can pretty much keep him stunlocked and dead in short order. Black Breeze will appear as the 2nd to last boss. Very rarely this stage will take place in a brightly lit Hidden/Nightmare area.
Hoarfrost Hollow Gauntlet
Dangerous enemies are the spinning axe bosses (like Raging Ekeloch) and variants like the gloomy boss from spider overload, and the boss from culprit behind the disturbance. Any one of these guys are very deadly if they have a swift or speedy modifier. The polar bear is the white tyrant version, so he's pretty soft and easy to kill. Polar Bear will appear as the last boss. You can hide in the small crevice in the main room to drink pots if needed - most large enemies won't chase you in there.
Ainle Gauntlet
Dangerous enemies are the Spark and Flicker, every other vampire is pretty easy to handle. A speedy, sly, or swift version of Spark or Flicker is quite nightmarish as they are able to flood the battlefield with sparks and waves of lightning. For some reason, I've never seen the goblin bosses (Kalis, Servant of Twilight, etc.) spawn in the gauntlet.
Save palalas for blood lord. BL has a ton of health and defense so he won't die nearly as easily, not to mention you're 4 manning it. If you're lv 50-55 and not in the best available gear I suggest sticking to normal so you can palala spam him to death, otherwise you're in for a very long fight with little room for error. The Blood Prince is always the 2nd to last boss, then the Blood Lord appears last. Blood Lord has a new trick that doesn't happen in the regular raid - his teleport hurts you if he appears next to you, enforcing the 'always keep moving' nature of the encounter. Probably the worst combination is thick skinned as you'll have to spend quite a long time killing him and lots of room for mistakes.
If you are not lv 60 with the best gear, I suggest playing on normal and carefully timing palalas and gravity inversions, unless you are all pro and you can 4 man BL over a long period of time without multiple deaths. It helps if the evies type G into party chat before using gravity inversion, so everyone can prepare to maximize DPS appropriately. Even when palala chaining without any wipes or graces or assists, expect the gauntlet to take 15-20 mins. Good luck if you get a speed boosted or vengeful Blood Lord.
Ruins of Sanctuary Gauntlet
I haven't tried this gauntlet yet, but the last boss is Laghodessa. Dangerous bosses in my opinion: Singleshot due to his fast fireball flips and ability to cover the screen with arrows. Fleeing Gnoll King due to his rampage ability. Giant Spider with his body slams and generally large hitbox. A speedy, sly, or swift version of any of those bosses will probably be a nightmare for your party.
Types of modifiers with descr1ptions based on my experience:
Educated - Occasionally blocks.
Speedy - Moves 2x faster, attack speed boost.
Sly - Attack speed 2x faster, attack speed boost.
Swift - Moves and attacks at 1.5x speed.
Poisonous - Applies poison DoT, attack speed boost.
Flaming - Applies fire DoT, attack speed boost.
Sharp - Always does the same attack twice. Does not apply to taunts or weakness animations.
Mastermind - Summons trash mobs. This is a good thing usually because for some reason every time the trash spawns, the mastermind boss will stop what they're doing and make a spawning animation (like the kobold roar or vampire ceiling drop) with the rest of the trash that just spawned. Just keep clearing the trash to keep it from doing much of anything.
Obsessive - Tends to target one person over all others.
Stoneskin - High def, high dmg, slower attack speed.
Thick-Skinned - Has a glow which turns on and off. When glowing it takes reduced damage.
Lady Killer - Extra damage to women, less damage taken by women, takes extra damage from men.
Man Hunter - Extra damage to men, less damage taken by men, takes extra damage from women.
Lethal - Extra damage, but lower DEF.
Vengeful - Randomly glows pink. When glowing pink, all damage you do to them is also caused to you. Avoid hitting them when they are glowing.
Blade Breaker - Extra damage to Lanns. Has a glow which turns on and off. When glowing Lanns do reduced damage?
Shield Crusher - Extra damage to Fionas. Has a glow which turns on and off. When glowing Fionas cannot block its attacks.
Spell-Eater - Extra damage to Evies. Has a glow which turns on and off. When glowing Evies do reduced damage?
Unstoppable - Stun resistant. Cannot be blocked, but can be heavy standered? (unconfirmed)
Explosive - Trash mob only. Explodes like a small bomb after dying.
Immortal - Trash mob only? Spawns other trash mobs when killed.