This paper proposes a novel Multi-Strategy Improved Snake Optimizer (MISO) to address the slow convergence rate and tendency to fall into local optima of the conventional Snake Optimizer (SO) algorithm. MISO overcomes the shortcomings of SO through an adaptive random perturbation strategy based on a sine function, an adaptive Levy flight strategy based on size coefficients and leaders, and a position update strategy combining elite leadership and Brownian motion. Using 30 CEC2017 and CEC2022 test sets, we compare MISO with 11 other algorithms and demonstrate its superior performance in terms of solution quality and stability. Furthermore, we apply MISO to 3D path planning for unmanned aerial vehicles (UAVs) and six engineering design problems to verify its practical applicability, confirming the effectiveness of MISO.