My credentials for this: I’ve fought Gabriel twice now, the first zone’s duel, and gotten him down to 40% before wiping due to greed.
The biggest note: If you do not have either Lost Manawall or (maybe, I did not confirm this) a tank invuln, do not accept the duel. You will fail, guaranteed, and steal the lottery ticket away from someone that might have had a chance to win.
Eligability: You have to get a gold ranking on the scorpion Critical Engagement without dying or gaining a vuln stack from hitting an AoE. If you eat an AoE with Hallowed or Superbolide, you will still be eligable.
Missile: Ground aoe at your location that leaves a void puddle that will kill you in one tick. Place these around the edge. Comes in sets of 5 or 6, they don’t persist forever but they do for quite a few minutes.
Dynamic Sensor Indicator (Or w/e the red debuff on you is): Stillness from TEA/the same debuff from Baelsar’s Wall. Do not move, auto attack, or use an ability until this debuff falls off (you can move until about the 2 second mark on it). This is always paired with three semi-random aoe markers near your location. There is enough time to move after the debuff fades, don’t panic.
Dashing to the edge: This is followed by a knockback,w hich can be negated with standard knockback tools. This is combined with later mechanics. Don’t get knocked back into a puddle you dropped.
Directional vulnerabilty from Mustadio in Orbonne: You will be surrounded at three quadrants on your target ring with one open quadrant. This is always followed up with a charge knockback. You must face your side without a pulsing yellow marker to the boss to not get one shot.
4-directional vulnerability: For the second directional vuln the boss does, and only this one, you will instead have all four directions marked as vulnerable. This is where Manaward or the tank invuln comes in. You must use these to survive. I don’t know if tank invulns work, I can confirm Manaward does.
Bahamut towers: All of the knockbacks after the first are paired with a tower you must get knocked back into. Standing a bit away from the boss will do this properly. Do not drop your lightning puddles in the middle as they might overlap a tower. The edges are always safe for those.
Cruise missiles: As in O7S. Missiles that lazily travel from their spawn across the arena in a straight line. As with all moving objects in XIV, their hitbox is a little ahead of where the visual indicates it will be. These always spawn in two lines of four that intersect in an X pattern.
Placeable proximity aoe: Indicated by a prey marker on you. When the prey expires, you will drop a proximity aoe where you are standing. The falloff on this is huge, you want to run far away from it. This always occurs during the cruise missiles. What I found successful was dropping my proximity aoe at the far side of the ‘X’ then running in a wide circle around the incoming missiles before slotting back in mid and running away.
Knockback with directional vulnerability into a tower.
Knockback with omnidirectional vulnerability and a tower (Use Manaward here while standing in the tower)
Cruise missile + proximity aoe
Three directional knockback towers
Cruise missile into proximity aoe
Repeat until enrage (I didn’t get this far to see what the enrage was, but it’s tight enough to require good play).
Again, the key takeaway from this is that the fight has a hard failure point that you will not pass without sufficient preparation. Do not steal queues from people that can succeed if you are not prepared.