Retarget skill for AI agents

​

When your agent uses it

• Applying existing animation clips from one rigged character to a different rigged character — sharing one animation library across models
• The same clips must play on several differently proportioned rigs without regenerating them

​

Install

npx -y summer-engine@latest skills install retarget --agent claude-code

​

The skill

​

There is no retarget MCP tool. Read this before promising one.

​

When to use this skill

• “I bought (or generated) one animation library — apply all clips to my five enemies.”
• “Goblin and orc have the same combat moves — share the library.”
• “I have 30 NPCs with the same idle / walk / talk loop.”
• The user generated motion on character A and now needs it on character B.

​

When NOT to use this skill

• The user wants ONE new clip on ONE character — just call generate-motion.
• The user wants to retime, edit, or layer the animation — that’s animation-tree and the procedural-animation additive layers.
• Target is a quadruped or non-humanoid (wings-only, mech, blob). The curated Meshy library is humanoid-only and SkeletonProfileHumanoid is a humanoid profile. Hand-author instead.

​

Path A — regenerate on the target rig (Meshy-rigged targets)

​

1. Find the source clip names

assets.search({ query: "<source character>", assetType: "animation", scope: "mine" })

​

2. Find the target rig

assets.search({ query: "<target character>", assetType: "3d_model", scope: "mine" })

​

3. Confirm with user before spending

I’m about to generate 12 clips (idle, walk, run, attack, …) on orc_rigged. That is 12 generations, a few minutes total. OK?

​

4. One generation call for all the clips

assets.generate_motion({
  rigAssetId: "<target_rigAssetId>",
  backend: "meshy-library",
  motionNames: source_clip_names   // exact curated names — see generate-motion's list
})
jobs.wait({ jobId: "<job.id>", timeoutSeconds: 50 })   // again until finished

​

5. Attach to the target’s AnimationPlayer

summer_set_resource_property(
  scenePath: "res://main.tscn",
  nodePath: "./World/Orc/AnimationPlayer",
  resourceProperty: "libraries/default",
  subProperty: "<clip_name>",
  value: "<animationAssetId>"
)

​

Path B — in-engine retargeting (non-Meshy rigs, bought or hand-authored clips)

1. Create a BoneMap resource per rig, with profile set to a SkeletonProfileHumanoid. Map each profile bone name to that rig’s actual bone name. Save as .tres — one per distinct skeleton, reused forever.
2. On import, set the source .glb’s import options to use the source rig’s BoneMap so its animation tracks are expressed against the humanoid profile.
3. On the target character, add a RetargetModifier3D under the Skeleton3D and set its profile to the same SkeletonProfileHumanoid. It re-projects the profile-space pose onto the target’s bones each frame.

​

Confirmation gates

• Before any generation call: show the full clip list and the number of generations.
• After the first clip: preview the result. If it looks wrong, stop the loop and re-evaluate (proportions, T-pose, missing bones).
• Before saving the scene: confirm the AnimationPlayer additions you’re about to write.

​

Reference card

​

Decision rule

​

Pitfalls

• Assuming a retarget tool exists. It does not. Check the tool list before promising a capability; a hallucinated tool name fails the call outright.
• Reusing the source animationAssetId on the target. Animation assets are bound to the rig they were generated against. Generate against the target’s own rigAssetId (Path A) or go through a BoneMap (Path B).
• Omitting scenePath. summer_set_resource_property, summer_save_scene, summer_add_node, and summer_set_prop all take a required scenePath.
• Mixing Meshy and Mixamo libraries on one character without a BoneMap. The bone-naming conventions differ; the AnimationPlayer plays tracks against bones that don’t exist. One rig provider per character, or map both through the humanoid profile.
• Proportion mismatch. A library authored on a 1.8m humanoid on a 2.5m ogre runs, but you get foot-float and limb-twist. Layer foot IK afterwards — see procedural-animation.

​

Quality bar

• Library authored on a 1.8m humanoid → target between 1.5m and 2.2m: production-ready.
• Target 2.2m–3m: expect foot-clipping; layer foot IK.
• Target < 1.5m or cartoon proportions (big head, short limbs): expect limb-pop.

​

Anti-patterns

• Calling a summer_retarget_motion / summer_retarget_* tool. None exists.
• Passing an asset ID to summer_inspect_resource. That tool takes a res:// path to a resource in the project, not a cloud asset ID. Use assets.get({ assetId: ... }) for asset metadata.
• Generating motion on each enemy separately when they are instances of the same rig. Instance the scene; the library comes with it.

​

Edge cases

• Source has facial blendshape tracks. Skeleton retargeting only handles bones. Facial tracks do not transfer. Hand off to facial-and-lipsync to re-author per character.
• Target rig is a different Meshy skeleton generation. Symptom: bone-count mismatch even though both are Meshy. Re-rig the target with a fresh assets.generate_3d({ kind: "image-to-3d", imageUrl: "...", rig: true }) call.
• The clip the user wants is not on the curated list. Path A cannot produce it. Either hand-author it, or import a Mixamo clip and take Path B.

​

Fallback (no MCP)

​

Handoff

• After the clips are on the target, the wiring is identical to a freshly-generated clip — hand off to character-animation-wiring for the end-to-end path (inspect the target’s real clip/bone names first — retargeted imports rename things), or animation-tree for blend-space/overlay graph design.
• If the result shows foot-clipping or hand-pen-through-prop issues, hand off to procedural-animation for IK correction.
• For NPC behavior driving these clips, hand off to design-npc.

​

See also

• generate-motion — the tool that actually produces clips, and the curated name list.
• asset-strategy — getting characters rigged in the first place.
• animation-tree — wire the clips into a state machine.
• procedural-animation — fix proportional mismatches with foot IK.

​

From a shell

​

Related skills

• character-animation-wiring: Wire a rigged character end to end: real clips and bones, locomotion states, method tracks, root motion.
• design-npc: Design enemy, NPC, boss or companion behavior: perception, state machine, telegraphs, script stub.
• animation-tree: Wire AnimationTree state machines and blend trees: locomotion blends, attack interrupts, hit reactions.
• facial-and-lipsync: Make a character’s mouth move with a voice-over: phonemes, viseme blendshapes, facial expressions.
• generate-motion: Attach a library animation clip (idle, walk, run, attack) to a rigged character via AnimationPlayer.
• procedural-animation: Runtime bone changes on top of clips: head look-at, foot IK, hand grabs a prop, lean, recoil.
• asset-strategy: Route any ‘I need a [thing]’ asset request to the right skill: 2D, 3D, audio, video, VFX or animation.