The Obscurus darted forward and Grindelwald quickly cast a wordless Protego, but he needn't have. The black cloud simply stroked lightly against the shield before darting away, disappearing under the child's wooden crib.
A loud knock came from the door he was still braced against, and Grindelwald commanded them away with a rough, "Leave," not needing to check to know his order was followed and instead creeping forward to where the Obscurus had vanished.
No sound came from it, though it was clearly there by the way it lightly rocked its own crib from below, the gentle sway so unlike what Gellert expected such a creature to be capable of, so unlike what Credence had shown.
"Hello, little one?" he called softly, crouching down so his slacks crinkled at the knees. "I mean you no harm," he said gently, hesitantly reaching a hand towards the dark confines below the toddler's cot.
A single strand of black wavered outwards in reply, and he stilled himself and avidly watched its movements, a silent shiver wracking up his spine at the numbingly cold touch of it against his outstretched finger.
Apparently emboldened by his lack of outward response, more of the mist crept out from the recesses, drifting forwards until Gellert's entire hand was enveloped in black, the chill of it fading away with exposure.
The black mass was constantly shifting even while remaining centered around his open palm, layers of it overlapping to form black as dark as pitch or lighter, less opaque hues that danced across his wrist.
"Aren't you a curious thing," Gellert breathed, stroking above the cloud with his unoccupied hand, fascinated in the way the creature seemed to flutter against his touch.
He carefully shifted himself so he was sitting more solidly, having grown uncomfortable in his previous stance, and the Obscurus seemed to take this as an invitation to trail up his arm, the mass of it settling over his middle, and then from one moment to the next, he had a lapful of child.
"Oh," he stated, somewhat taken aback, and, after taking a fraction of a moment to process the abrupt shift, he gave the young boy a sliver of a smile and grasped him gently underneath his arms.
The tot still wore a rather pleased expression, eyes impossibly large and gleaming Avada Kedavra green to the point where they nearly seemed to glow, and a small hand reached forward to grasp at his cloak. Gellert was quite sure he'd never felt so befuddled in his entire life, though he kept it from outwardly showing.
"Would you like to come with me?" the Dark Lord suggested lightly, bouncing the child slightly and earning a small giggle in return; the toddler peered up at him, giving no real response, though that was rather expected.
Gellert shifted to grasp the child more firmly in his hold and stood, settling the blonde - the pale color of it eerily reminiscent of Gellert's own - on his hip.
Then he gave a single, decisive nod, and apparated away.