Brynhild (Berserker)

Most Masters are looking to use Brynhild for damage and should prioritize giving her the most damage on a single shot. By boosting up her 2nd skill’s charge to max and adding damage with her 3rd skill, her offensive capacity is enabled to its fullest. Her first skill can generally be left alone as Damage Cut won’t make much of a difference for her.

• Swan Dress (Summer) A+ gives Bryn both a damage cut and an evasion, both turn and usage limited. In practice a Master wants to use this the first turn she could expect to take damage to leave her out as long as possible before her low durability kicks in. Masters might want to level this to max if they want to make use of its short 5-turn cooldown against 3-turn effectiveness, but most can leave it alone and level it last. 
• Wisdom of Summer B is Bryn’s crucial skill thanks to its 20% charge per turn. Bryn will not likely be generating much Noble Phantasm gauge on her own, so this serves in its place. Masters will want to pop this as soon as they can and as often as they can as Bryn’s kit is mostly her Noble Phantasm. It does generate a small pool of Critical Stars as well, although her star gather is so low she’ll likely not benefit from it herself. Level this first and to max, as the charge per turn can make all the difference. 
• Summertime Lovers EX serves as both a notable steroid in Arts and Buster for Bryn and for any allies with the Loved One trait (nearly all males and a few females). While this is generally popped on her Noble Phantasm turn, it could be used as a buff for her allies for the rest of the match after she’s off the field. Level this second to any level one feels comfortable with, as it gives power with every level. It is the obvious 2nd level choice. 

“I’m sorry if I end up hurting you..”

Brynhild, the chief of the Valkyries, is well known for wanting nothing more than to kill Sigurd whenever she sees him. Remove her bloodlust and you get a Berserker in a swimsuit wanting to shower Sigurd with love. Fate logic. As an AoE Buster Berserker, Brynhild offers a steady widespread damage pool for Masters needing a Servant with Ignore Invincible.

Bryn’s biggest strength is her Noble Phantasm. With Ignore Invincible, which activates before damage, and Berserker advantage against (almost) all enemies, she is capable of handling many of the trickier matchups she’d face. Thanks to the powers of Wisdom of Summer she can charge her NP gauge with little difficulty, while creating a small pool of stars for use. She also can serve as an auxiliary support for males (and a couple of females) with her Summertime Lovers card boost.

Unfortunately, while her Noble Phantasm is unavoidable, it also is particularly weak. With only Madness Enhancement D- and fairly low boosts to her Buster Cards on Summertime Lovers and her Noble Phantasm’s overcharge, she’ll struggle to pack the required punch. Her durability is also questionable with 

Swan Dress (Summer)’s limited evasion serving as her entire endurance set. Without it, a single critical hit could take her out.

Bryn is a decent option for a Master wanting Ignore Invincible or extra support for Arts or Buster based Male Servants. But since her 2nd ascension’s swimsuit is so damn cute, all Masters would want her anyways!

Ignore Invincibility

While most Servants with an Ignore Invincibility effect have it as a skill with cooldown, Bryn’s activates every time she uses her Noble Phantasm. To make matters better, it’s a 1-turn pierce instead of a 1-time, meaning any attacks she does after her Noble Phantasm will have the same effect. This could add some consistency to runs using her regardless of enemy skills.

Decent NP Charge

In theory, Bryn can generate 60% gauge over 3 turns, enabling most mixed CEs to work with her on longer fights. If a Master unlocks her Mana Tuning Append skill, she only needs 2 turns to reach maximum gauge so that she can unleash her NP on the 3rd wave (which may often fall on the 3rd turn). Her non-skill based NP gain is not particularly good, being a gorilla style Berserker and not having particularly notable hit counts, so most Masters should expect to use her as a one-and-done.

Support

While not a common usage, Bryn could be used as a support Servant thanks to her ability to provide up to 30% Arts and Buster boosts to any Loved One ally. This 3-turn boost for all members of the party is one of the highest available.

Mediocre Damage

Bryn’s damage suffers as she doesn’t have access to any ATK or NP damage buffs. Further, as a Berserker she will not pull critical stars, so her sustained damage drops dramatically. Among 4-stars Berserkers she is one of the strongest, but this isn’t saying much. In most cases, a 2x class advantaged Servant would end up being a stronger option.

Low Endurability

Bryn’s first skill offers her a 2-hit evasion and a 3-hit flat damage reduction. While the evasion is welcome, the damage reduction will likely do nothing after taking double damage. With her low HP, she likely can only take 3 or 4 hits (evasion included) before she leaves the field.

Brynhild’s Noble Phantasm will likely be used once in a match and increases in power with Overcharge, so a CE with an Overcharge Effect is one of the most powerful she can use. Noble Phantasm Damage CEs are also effective for her if she has support at the cost of whittling down her already weak constitution. Barring those, a Mixed Damage / Starting Gauge CE is as effective as ever on a damage dealer.

• Devilish Bodhisattva: Bryn’s overcharge effect is more Buster damage, and DB has the distinction of providing 60% charge at MLB. This would allow Bryn to fire her Noble Phantasm on the third turn using her second skill with no support needed.
• The Black Grail: If Bryn has support she could boost her damage output further than DB using a Black Grail. However without support she’d likely never get the 100% charge she needs even with her second skill.
• Partake with the King/Aerial Drive/Holy Night Supper/Golden Sumo:Bouder Tournament/Curse of Love: As a damaging Servant, Bryn can benefit from both a starting NP gauge and a damage boost making mixed CEs quite usable. Partake with the King in particular is powerful at MLB as it allows her to NP on the 3rd turn with no extra gain than her 2nd skill. All others will need at least a 10% gain.