Arabella Builds/Thoughts (AOE, Single Target, Not much fracture needed)
Intro/Thoughts:
Fracture Mechanics: The way fracture works is that it does a single hit based on the stacks but the damage is also determined by the unit's stats like atk, crit, dmg over time and buffs or debuffs like morale, damage amount and reduce fortitude. This could very easily be an extra hit or extra attack and it wouldn't be much different. When fracture triggers the stacks will be reduced by half rounded down.
Fracture amplification (FA) gives 1 or 2 stacks (if aoe or single target) to fracture when fracture tiggers. For example if the enemy is alone with FA and has 6 stacks, if we trigger fracture 3 times manually and then end turn then the stacks will change as follows: 6 --1st--> 3+2 = 5 --2nd--> 2+2 = 4 --3rd--> 2+2 =4 --end--> 2+2=4. As you can see the enemy will never run out of stacks as long as it has FA and any amount of fracture. Same thing happens to the FA target at AOE but with slightly less stacks.
Thus, instead of trying to get multiple stacks of fracture, then detonate them, and repeat which would require alot of sequencing, a harder build and buffs that favor big multipliers it's just easier to apply fracture and FA once and just spam detonate it with morale stacking and similar effects.
Her AOE cards that detonate aplly fracture so this is not an issue for aoe as well.
Is Arabella DOT reliant? The observations above mean that for some builds fracture is not really treated as a dot in a traditional sense but as a hit that doesn't count towards elasticity. Even in content that have no dot synergies/shill she can do fine. I didn't run the numbers to tell you if she is broken or not but she can work just like any other unit without worrying about her becoming unplayable after 1 season. She is only unplayable if the enemy cant be debuffed/dot
Is Hilde needed? Hilde is not really needed but she does work well with her. She is basically Veronica+ for Arabella. It's not really about the fracture arrows, she just has good draw, decent damage, ionisation which benefits all of her builds and also hilde's fracture triggering at the end of turn gives some stacks (counted as arabellas stacks) to the target with FA. I am not sure how relevant this is but it is marginally a benefit.
Builds:
All of my units are E0 (Mika E6), and the partners are Scarlet for Arabella, E4 Rosaria for Hilde and E5 Arwen for Mika. These builds might not and probably aren't the bis builds you could do since season 3 has some stupid stuff especially for strikers but it's something easy to play and build as long as you don't mind farming the sortie divine cores. These aren't really optimised for leaderboards just something I made to use in AOE and Single Target with Arabella.
AOE:
For aoe I used this build that wants to go Claim 3 control 5 to get +20/25 cr from control 5 and the morale from claim. Other cards are Driven hunt Survival/Control 2 on Hilde/Veronica and Kneel before me Control 3 on Mika.
For Hilde you could change some cards like quivers and plasma rain to different epiphanies, I just got those and rolled with it. This draw and release was the best epiphany for card draw and you get free fracture as bonus. Not sure how much the aoe fracture matters without the observer's pleasure that moves it around. Hilde's necklace helps to get some extra utility in aoe.
For Arabella I used a different observers pleasure when I was doing FSA, I would either do the 30% dmg per enemy or 80% total and move fracture around. With Veronica I would probably go for the first one. Hollow Verdict is the most important card here the rest could have the epiphanies that you like.
Single Target:
Similar build for the supporting members with different desire cards.
Survival 5, claim 3 for +9 morale. With mika and rosaria you could reach 14-15 morale. Also with the Desire cards you can reach -3 fortitude on enemies and +120% on Arabella's dmg.
The upgrade observer's pleasure is very strong giving you free FA and 6 fracture to work with without having to draw anything. You ideally want to use hollow verdict once before using the Sadistic restraints because they scale with fracture detonations. As stated at the start of the post you never run out of fracture and Sadistic Restaint is basically an 8 hit card that bypasses elasticity. Both support units could be replaced with someone else that draw + give AP.