Conversation so far:
What was a famous work of Paul Klee's that came out during the Mystical-abstract period?
Paul Klee created abstract works in that period such as Abstract and Farbige Kreise durch Farbbänder verbunden.

Question: What other painters were famous during this period?
Self-contained rewrite: What other painters were famous during the Mystical-abstract period, besides Paul Klee?