Unity 2D Animation

Two animation styles

You can mix: skeletal for body + sprite swap for facial expressions.

Frame-by-frame

Sprite Mode = Multiple → Sprite Editor → Slice (Grid by Cell Size or Automatic)
Drag the resulting sprite sequence into Animation window → Unity creates an Animator + clip.
Loop time: ON for idle/walk; OFF for one-shots (attack hit).
Sample Rate: 12 fps for retro; 24 fps for smoother.

Skeletal 2D

Required packages: com.unity.2d.animation + com.unity.2d.psdimporter (or Aseprite).

Workflow:

1. Author character with each part on its own layer in Photoshop (.psb) or Aseprite.
2. Import → PSD/Aseprite Importer creates a multi-sprite asset; Mosaic + Character Rig ON.
3. Open the prefab → Sprite Editor → Skinning Editor.
4. Add bones (root, spine, head, arm_L, arm_R, leg_L, leg_R).
5. Auto-Geometry creates mesh; Auto-Weight skins vertices to bones (review/repaint with brush as needed).
6. Drag the prefab into a scene → it has a SpriteSkin per part.
7. Animation window → record bone Transform changes; Animator state machine drives clips.

IK (com.unity.2d.animation)

For arms/legs: add Limb Solver 2D (two-bone IK) on the IK Manager:

ChainSize = 2 (upper + lower arm)
Target = empty Transform you move; the limb chain follows it

Procedural foot placement, mouse-aim arms — both classic IK use cases.

Sprite Library / Resolver

For runtime outfit swaps without re-skinning:

1. Create a Sprite Library Asset with categories (Hair, Torso, Legs) and labels per category.
2. On each body part GameObject, replace SpriteRenderer.sprite with SpriteResolver referencing a category+label.
3. At runtime, change SpriteResolver.SetCategoryAndLabel(category, label) → swaps sprite without losing skinning.

PSD Importer

Settings to know:

Texture Type      Sprite (2D and UI)
Sprite Mode       Multiple
Mosaic            ON   (packs each layer into the atlas)
Character Rig     ON   (creates a bone-rigged prefab)
Use Layer Group   ON   (preserves PSD group structure as bone hierarchy)
PPU               match project-wide PPU

Re-import after a PSD edit → bones + sprites stay in sync; skin weights are preserved.

Aseprite Importer

Same idea but native Aseprite (.ase/.aseprite) workflow — preserves layer groups, pivots, and animation tags (importing as separate AnimationClips automatically).

Use .aseprite for pixel-art characters; .psb for hi-res / hand-drawn.

AI-assisted animation (the hard part of AI sprite gen)

Generating a single sprite is mostly solved; generating a coherent 8-frame walk cycle, 4-directional turn, or attack-with-trail animation is still where most AI tools fail. As of 2026 only one tool produces directly-usable animation end-to-end inside an Aseprite-friendly workflow.

The current state of play

Recommended workflow

For simple multi-direction characters (top-down RPG, action):

• Generate full set in PixelLab → export sprite sheet → import into Unity, slice in Sprite Editor → create Animation clips (Idle / Walk / Run / Attack) per direction → Animator with float MoveX, MoveY parameters + blend tree. See "Frame-by-frame" section above for the clip mechanics.

For metroidvania / detailed side-scroller characters:

• Generate base character in Retro Diffusion (or Aseprite-painted) → import into Unity 2D Animation as multi-sprite (Mosaic ON, Character Rig ON via PSD/Aseprite Importer, see PSD Importer section) → rig bones manually in Skinning Editor → Auto Weights → animate clips by keying bone Transforms. AI handles the art; you handle the rig.

For high-end / signature characters:

• Train a Scenario.com character model on 10–15 reference images of the protagonist → generate every key pose / costume variant on-model → assemble sprite sheets manually → either import as multi-sprite (frame-by-frame) or rig in Spine + spine-unity for runtime skeletal animation.

Tradeoffs at a glance

Hybrid pipeline (most pragmatic)

Buy Retro Diffusion Full ($65 once) as the everyday static-asset tool, plus one month of PixelLab ($12) when you need a sprite sheet animation sprint. First-year total ~$77 for a full indie-grade character + tileset + animation pipeline. After year 1, only Retro Diffusion runs ($0 ongoing) unless you renew PixelLab for new animation work.

Critical caveats

• AI walk cycles are acceptable for prototypes / game jams but typically need 1–3 hand-fixed frames (anticipation, hit frame, follow-through) before shipping.
• Multi-direction consistency is fragile — PixelLab's 4/8-direction rotation works best on chibi / front-facing characters; complex silhouettes (big weapons, capes, animals) often need touch-up.
• Sprite Library + Sprite Resolver (see section above) lets you use one AI-generated rig for many character variants by swapping sprites at runtime — high ROI when paired with a custom-trained Scenario model.

For the static / single-frame side of AI sprite gen (props, tiles, items, environments), see the unity-2d-core skill's "AI-assisted sprite pipeline" section.

Anti-patterns

Production checklist

• PPU consistent across PSDs/Aseprite imports
• Character rig auto-created via PSD Importer (Mosaic + Character Rig)
• Skin weights reviewed at deformation joints (shoulders, hips)
• IK used for limbs that need targeting
• Sprite Library + Resolver for variant systems (skins, outfits)
• Animation events (AnimationEvent) used for hit frames, footsteps