No MMORPG is fully complete without having an enormous creature to try and bring down with ingenuity, and lots of firepower. That is what the Guardian Raids are for.
Guardian Raids in Lost Ark are instanced Boss fights, in which players are tasked with finding and defeating the so-called Guardians. This is a step-up from the Chaos Dungeons end-game content, and we recommend only attempting them once you've completed a few of those.
Just like the Chaos Dungeons, the Guardian Raids can have up to four participating players. Unlike the Chaos Dungeons, however, it is very possible to fail these, and we recommend not soloing them, as the rewards are the same whether you are alone or with a group.
Once you spawn in the Raid, you have 20 minutes to track down and kill the Guardian Boss. You do this by activating flares on the map to mark the spot where the Guardian is, for other players to see. There is a limit of three respawns for each Guardian attempt, so make sure you don't die for no reason, as you can't spam the Raid infinitely.
Smilegate
Guardians are the hardest fights you will have encountered in the game at that time. They are the only monster that has no health bar, and fighting them is centered on finding opportunities for DPS, without being crowd control locked by the Boss' abilities.
In short, Guardian Raids are the Dark Souls content of Lost Ark, and you can't expect to mow them down as you would the most of the game's other mobs.
