Animation retargeting broken on new SKM_MHC MetaHuman skeletal mesh (UE 5.7)

[Owl_Snowy]

I’m having an issue with animation retargeting using the IK Retargeter in UE 5.7 and I’m hoping someone can help me understand what’s going wrong.

Setup:

• Source Skeletal Mesh: SKM_UEFN_Mannequin
  

  

• Target 1: m_med_nrw_body_mocap (MetaHuman from GASP/Kellan preset) — retargeting works fine
  

  

• Target 2: SKM_MHC_Wayne_BodyMesh (MetaHuman created by me in MetaHuman Creator, UE 5.7) — completely broken/deformed result
  

  

• Both targets share the same skeleton (metahuman_base_skel)

• Auto Generate Retargeter is enabled on both

The problem:
Since the warnings are identical on both targets but only the new SKM_MHC mesh is broken, the warnings don’t seem to be the root cause.

My suspicion is that the new has a different Retarget Base Pose baked into the skeletal mesh asset compared to the older m_med_nrw_* format, even though they share the same skeleton. The IK Retargeter appears to be sensitive to this difference when using Auto Generate.

Question:
What is the correct workflow for retargeting animations onto a MetaHuman created with the new MetaHuman Creator in UE 5.7?

[Owl_Snowy]

How I fixed the hand deformation on a custom MetaHuman with GASP

I managed to minimize the hand deformation on my custom MetaHuman. The key is to correctly transfer animations from SK_Mannequin to SK_UEFN_Mannequin and set up proper IK Retarget files.

This will likely affect everyone who wants to use GASP with a custom MetaHuman, so here are the steps that worked for me:

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STAGE 1 — Retarget animations to the UEFN skeleton

1. In the GASP files, find IK_UEFN_Mannequin and create an IK Retarget asset from it.
   

   

2. In the Details panel of that file, set Source to IK_UE5_Mannequin_Retarget and Target to IK_UEFN_Mannequin (swap the preview skeletal meshes if needed).
   

   

3. In the Hierarchy tab, click Target → Auto Align → Align All Bones. This aligns the UEFN skeleton pose to match the Mannequin skeleton.
   

   

4. In the Op Stack tab, delete all auto-generated Ops, then click Add Default Ops again. This recreates them with the correct settings.
   

   

5. In the Op Stack tab, add a new Op: Scale Source, and set the Source Scale Factor to 0.935 so both skeletons match in size.
   

   

6. In FK Chains, for all Thumb and Metacarpal chains set the Rotation Mode to Copy Local.
   

   

For Thumb chains also set Translation Mode to Orient and Scale.

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STAGE 2 — Retarget animations from the UEFN skeleton onto the in-game MetaHuman

GASP itself recommends using ABP_GenericRetarget to drive MetaHuman animations at runtime.

1. In the GASP files, find IK_Metahuman_Retarget and create an IK Retarget asset from it.
   

   

2. In the Details panel, set Source to IK_UEFN_Mannequin and Target to IK_Metahuman_Retarget. Set the Target Preview Mesh to your custom MetaHuman skeletal mesh.
   

   

3. In the Op Stack tab, delete all auto-generated Ops, then click Add Default Ops again to recreate them with correct settings.
   

   

4. In the Hierarchy tab, click Source and go through each bone, setting its Transform Bone values to 0 0 0. This puts the UEFN skeleton into a clean T-Pose.
   Some bones require specific rotations:

   pelvis       0   90    0
   clavicle_l   0  -90    0
   hand_l     -90    0    0
   thumb_01_l   0  -45    0
   clavicle_r   0  -90  180
   thumb_01_r   0  -45    0
   thigh_r      0    0  180
   

5. In the Hierarchy tab, click Target → Auto Align → Align All Bones. This aligns the MetaHuman skeleton pose to match the UEFN skeleton.
6. After this, the metacarpal bones of the hand should no longer collapse/merge. You can further fine-tune the result by manually adjusting the rotation of specific MetaHuman bones as described in step 4.
   
   

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Hope this helps someone!

[Owl_Snowy]

Result