I quilt with a single thread, as do all hand quilters I know of. I like to wax my thread with bee's wax, for ease of pulling.
I spy usually suggest a quilt made with many interesting novelty fabrics, fussy cut so that they are featured. The idea is that a child can spend hours searching for items or characters on the quilt.
Mystery quilts are often a group or class project where the makers do not know the final pattern or appearance of the quilt, but follow along each step at a time. Hence the mystery.
Tube quilting is not my topic and I'll leave it to others.
RST