Unreal doesn't author the motion — it retargets it. Animation is created elsewhere (hand-keyed in Blender, captured via mocap, or bought), and Unreal's IK Retargeter maps it onto your character using the IK Rig from Phase 2. Because every character shares one canonical skeleton, a single animation library retargets onto all of them — and the socketed prop follows the hand for free. The authoring side is on the Blender Phase 4 page.
The IK Rig you built in Phase 2 is the socket the retargeter plugs into. From there, any source animation on a compatible rig can drive your character.
Bring FBX animation in on the canonical skeleton (baked from Blender, or from mocap / marketplace). It becomes an Animation Sequence.
Set a source and target IK Rig and the IK Retargeter maps motion between skeletons — so animation authored on one rig plays correctly on your character's proportions.
Because the cast shares a canonical skeleton, a single set of walks, idles and gestures retargets onto every character — this is the whole reason to standardize the skeleton in Phase 2.
A still is a single-frame pose. And a held prop attached to the hand socket (Phase 3) rides the wrist through any animation — you never keyframe the prop.
The retargeter reads bone transforms. If the incoming animation still depends on a rig's IK controllers or constraints (un-baked), it arrives frozen or in a T-pose.
Fix: bake the animation to keyframes on the deform bones before export — done on the Blender side (Phase 4) — then import and retarget.
The IK Retargeter now has a full lesson: Retargeting with the IK Retargeter in the intermediate Cinematic Production track builds the IK Rigs, maps the chains, fixes the retarget pose, and exports a library. Authoring or correcting that motion by hand, rather than importing it, is covered in Animating with Control Rig. This page maps where the step sits in the pipeline; Character Movement is the nearest introductory foundation.
One canonical skeleton + IK Rig means Daz-derived characters can use mocap and marketplace animations interchangeably. The investment in Phase 2 is exactly what makes this phase cheap.