This paper introduces FedDance, an efficient and intelligent participant selection framework tailored to tackle the dynamic nature in FL. FedDance employs a lightweight stochastic prediction method to anticipate the dynamic availability of each device. To address the diminishing marginal returns from frequently selected devices due to training dynamics, especially in later training stages, FedDance explicitly quantifies the marginal return of each local training process over time. Additionally, FedDance incorporates a lightweight model to characterize data heterogeneity, enhancing the advantages of managing device and training dynamics. Extensive experiments conducted on four A100 GPUs demonstrate that FedDance can substantially outperform the state-of-the-art systems in final model accuracy and convergence speed, while also providing a considerable advantage in computational overhead.