General overview

Bagpipe increases the initial SP of all vanguards just by being on your squad. This on its own makes her an extremely valuable operator, but on top of it, she has very good DPS for a vanguard (and even for a guard, in some situations). In maps with a tough first wave of enemies, she can stall for DP for longer without being overwhelmed. (Don't forget she refunds her own DP cost!) No matter what you use her for, she carries a lot of weight, and it's well worth slotting her into a lot of teams.

E2? Strongly recommended because of her talent 2. She shouldn't be prioritized over core DPS (and you can always borrow her from supports if you need to), but having an E2 Bagpipe of your own frees up your support slot for other operators.

Talents

Talent 1 (Precise Reloading) gives Bagpipe's attacks a chance to crit and hit an additional target. The odds are pretty good on their own (25%), and she gets even more opportunities for this talent to proc with her S2/S3 because her attacks hit multiple times.

Talent 2 (Martial Condition) gives all vanguards +6 initial SP when she's in your squad. This will speed up the beginning of a map significantly, especially in challenge maps with reduced DP generation, and it lets Bagpipe herself get her skills up faster as well. She gets an additional boost to this talent at Pot5 (+8 instead of +6 SP), which is a nice perk but not necessary for most players.

Skills

S2 (High Impact Assault) is an auto skill that increases the ATK of the following attack and has it hit an extra time. It also holds charges so she can unload a lot of damage on one enemy if one skill activation isn't enough to kill them. This is a good consistent laneholder skill if you just need her to take out weaker enemies or catch leaks.

S3 (Locked Breech Burst) is a burst skill that essentially turns Bagpipe into a guard for 20 seconds. Her attack interval lengthens, but in return, she gets an extra block, a massive ATK/DEF buff, and her attacks now hit 3 times in a row. The attack multiplier is already great on paper, made even better by the fact that she attacks 3 times in a row (which also synergizes well with her talent.) This skill is a great early wave clearer, but it also lets her take on pretty strong enemies if you leave her on the field.

Masteries

S2 receives an extra charge at M2, and that's where you'll probably be fine stopping. Masteries on S2 also help with her multipliers, but if you really want to punch up her DPS, you'd be better off prioritizing masteries on S3 instead. S3M3 more than doubles her attack, which is a massive DPS boost. The increased initial SP has even more of an impact with her talent 2 because she effectively gets 31 initial SP, so you don't even need to wait 10 seconds before her first skill activation.

Modules

Both of Bagpipe's modules are only worth it if you like using her as a unit in her own right and not primarily as a means to buff your other vanguards.

Module X gives you 2 DP after Bagpipe defeats an enemy (instead of the original 1 DP), and she refunds her current DP cost on retreat instead of her original cost. The upgrade affects talent 2, but it only gives Bagpipe herself additional initial SP. It's well worth it if you like to use Bagpipe as a helidrop.

Module Y increases Bagpipe's ATK to 115% when she attacks enemies with less than 40% HP. The upgrades give talent 1 a better probability of activation and a slight multiplier increase on the crit. This module is better if you want to leave Bagpipe on the field for DPS.