SCAIL-2 In-Video Character Replacement (WAN 2.1)

SCAIL-2 (zai-org, on WAN 2.1 14B) replaces the person in a driving video with a character you supply as a reference image, end-to-end, with no pose maps, and with multi-character support. It is the successor to WAN Animate / motion transfer for the "swap the subject, keep the motion" job. The official ComfyUI template is video_wan21_scail2_character_replacement_int8, built around WanSCAILToVideo (+ SCAIL2ColoredMask) with a SAM3 mask driving where the character goes.

This skill documents the non-obvious behaviours that cost a full multi-minute render to discover. It is not a from-scratch graph. Start from the official template and apply the guidance below.

The one rule that costs a re-render: reference framing controls SCALE

In replacement_mode: true, the reference image's FRAMING controls the output character's SIZE as well as its appearance. The SAM3 mask controls where the character is placed; the reference image controls how large.