Paramount Animation has historically operated as a front-end creative studio, partnering with external vendors to execute CG workflows through final delivery. For “Avatar: The Legend of Aang,” the production demanded a hybrid visual style—blending CG rendering, 2D hand-drawn animation, and 2.5D projection-based treatments—that no single vendor could deliver end-to-end. We stood up an entirely new internal back-end pipeline spanning ingest, compositing, effects, layout, and rendering in under five months with a 5-person TD team supporting 62 artists at a studio with no prior back-end experience. This paper presents FLO, a USD-to-Nuke assembly system; vendor-aware ingest validation; Nuke-side tooling for path-agnostic compositing, hand-drawn timing, and shot localization; Houdini USD FX integration; and Deadline render-farm automation. We report results across ∼1,500 shots and share tradeoffs and lessons learned.