This is level 1 of the New Tunnel.
In this tunnel, since you can only use the Duplicator and the Child in this tunnel at first, so the character suggestion's choice will only be the Duplicator and the Child. Please be aware of this.
In this level, there are many small platforms made by only one tile. Normally it would be very hard, but fortunately, the tile size is very large too. Therefore the gaps would be extremely large too.
Using the Child, you need to jump high and try to maintain in midair. As for the Duplicator, keep jumping off duplicates in the air, and try to remain in air for the whole level.
There is a cutscene featuring in this level. More cutscenes can be seen here.
Self Assembly Edit
Upon clicking on the first level of the New Tunnel, a cutscene will feature the Child and the Duplicator, standing on an edge (the edge of Low Power Tunnel, part 15). The Child noticed a tunnel branching out and sought the fact that there were floating tiles everywhere and starts to form a tunnel. The Duplicator said the tunnels are alive, and the Child is thinking that's a "baby tunnel". The Duplicator then jumps into the tunnel saying that they could be listening to us, and in the tunnel. They were told that we can talk there, and newborns don't understand speech.