Recent advances in dance generation have enabled automatic synthesis of 3D dance motions. However, existing methods still struggle to produce high-fidelity dance sequences that simultaneously deliver exceptional realism, precise dance-music synchronization, high motion diversity, and physical plausibility. Moreover, existing methods lack the flexibility to edit dance sequences according to diverse guidance signals, such as musical prompts, pose constraints, action labels, and genre descriptions, significantly restricting their creative utility and adaptability. Unlike the existing approaches, DanceMosaic enables fast and high-fidelity dance generation, while allowing multimodal motion editing. Specifically, we propose a multimodal masked motion model that fuses the text-to-motion model with music and pose adapters to learn probabilistic mapping from diverse guidance signals to high-quality dance motion sequences via progressive generative masking training. To further enhance the motion generation quality, we propose multimodal classifier-free guidance and inference-time optimization mechanism that further enforce the alignment between the generated motions and the multimodal guidance. Extensive experiments demonstrate that our method establishes a new state-of-the-art performance in dance generation, significantly advancing the quality and editability achieved by existing approaches.