You are on a slab in the void. Look up: there is a bucket. In your pocket, a few packs of masons. Lay a pack on a plane and it grows a bismuth crystal from there, brick by brick, freezing whatever was still growing — the plane you choose is the platform for the next growth. Climb it as it grows. Deploy again from higher up. Get above the bucket and drop in.
W A S D walk
space jump one layer
mouse look
E / right click deploy the pack on the plane you aim at (or underfoot)
click break a brick
1–6 / scroll choose a pack
F hold to grow faster
R start the level over
V in a replay: their eyes or your own
on a phone: the left stick walks, dragging the right half looks, the buttons do the rest
The bucket has you. The crystal stays as you left it; the next level is a new slab, a new pocket, a higher bucket. Your run is a record now: a few kilobytes that replay the whole crystal anywhere. Share it, watch it through your own eyes, or hand the crystal to someone to continue.
Someone's run, carried in the link. Watch it through their eyes as the crystal grows the way it grew. Continue it: their crystal, frozen where they left it, with your own full pocket. Or play the level fresh.
That was their run. The crystal is as they left it.