Fiora victorious in trifarian warcamp get falling star how the layering works

Yes — Fiora takes the full 6 damage and dies, and the caster has to pay the Deflect cost twice to even target her.

Here's the layering: Trifarian War Camp's +1 Might is an Arithmetic-layer effect (Rule 477.3), while Fiora, Victorious's "While I'm Mighty…" is an Ability-Altering effect (Rule 477.2). Layers loop (Rule 476): after Arithmetic puts her at 5 Might, the Ability-Altering layer is re-checked and she gains Deflect, Ganking, and Shield — so she's Mighty and fully keyworded. Since Shield only grants +1 Might while defending, she sits at exactly 5 Might outside combat.

Falling Star chooses a unit twice, so both instances target Fiora → Deflect 1 must be paid per targeting, adding 2 Power to the spell's cost (Rule 809.1.c). If the caster pays it, she takes 6 damage vs. 5 Might, which is lethal (Rule 143.2.a).