Once you're past the campaign, GFL2 is a question of where to spend pull currency and upgrade resources. This guide covers pull priority and the systems (keys, attachments, Neural Helix / Fortification) that turn a doll from usable into meta, from community consensus, reworded. The Keys & Affinity and Neural Helix & Fortification guides go deeper on each.
Pull priority
Support before DPS. GFL2 has few real supports and they never fall off — Springfield, Suomi, Vector, Mechty are the game-changers. A great support makes every DPS you own better.
Then your element's carry — Qiongjiu / Sharkry for Burn, Tololo for Hydro, Klukai for Corrosion, Makiatto for Freeze.
Standard-banner meta dolls (Qiongjiu, Tololo, Sharkry, Peritya, Faye) you'll get for free over time — don't spend limited resources targeting them.
Limited units worth the pull: Springfield, Klukai, Vector, Suomi. Skip most others unless they're for the element you main.
Expansion keys
An Expansion key (community shorthand: 'mod key') is a mid-life upgrade that can transform a doll — Tololo went from an occasional extra turn to one every turn; Sabrina went from pure tank to a DPS; Springfield's adds to her kit.
It's a reason to keep and invest in a doll you already run — rarely a reason to pull a new one. It's unlocked with a dedicated event/shop item, not raw dupes.
The Tier List notes where an Expansion key is the reason a doll sits where it does; each doll's Recommended build box shows her own.
Some dolls' keys do little (Nagant, Krolik) — don't chase those.
Common keys
Common keys are cheap loadout swaps that tweak a doll's kit — added cleanses, random buffs, extra movement.
Notable: Ksenia can be turned into a pseudo-Cheeta (random ally buffs) with the right common keys; several supports gain a team cleanse.
These are low-cost and worth experimenting with once your main team is built.
Attachments
Each weapon takes four attachments that roll main + sub stats — attack, attack boost, crit rate, crit damage and so on. Three matching attachments activate a Set Effect; the fourth slot is free.
Sets: run the +20% element-damage set (Burn Boost, Freeze Boost, etc.) on a pure element carry, Phase Strike (+15% vs any phase debuff) on a flexible one, Ballistic Boost on Physical dolls, Ultimate Pursuit on Ultimate-reliant kits, Emergency Repair on main healers, Ally Support on Bulwarks. Each doll's Recommended build box names hers.
Roll attack / attack boost / crit rate on every slot, then crit damage once crit rate is ~60–70%. Supports want whatever their kit scales off — a badly geared support still works.
Don't perfect-roll for a doll you're unsure about. Get her to 'good enough' and move on — this is the long-term grind, not a rush. Military and Precision attachments can be Calibrated (and Extreme-Calibrated for a chosen stat) once you're settled on a doll.
Neural Helix & Fortification
Two different systems. The Neural Helix is a 13-node stat / Key grid (unlocked at Commander Level 15) — rush its Evolved nodes for the Fixed Keys, leave the plain stat nodes for last.
Neural Fortification is the dupe-fed skill upgrade — V0 to V6, each level adding a clause to one skill. It's what the tier list means by 'V6'.
Fill the Helix Evolved nodes for your main team early; push Fortification only to each doll's first skill-changing clause unless you're swimming in copies. Full detail is in the Neural Helix & Fortification guide.