You're a Senior Risk Model Validation Manager at a large investment bank. Your team is tasked with validating a newly developed VaR engine. This engine is intended to replace the existing system and incorporates more advanced methodologies, specifically Monte Carlo simulations and high-dimensional Copula functions, to better capture tail risk and complex asset correlations. Walk me through how you would design and execute a comprehensive validation framework for this new VaR engine. In your explanation, please detail the critical steps you'd take to ensure its accuracy, stability, robustness, and compliance with regulatory requirements. Furthermore, outline the key challenges you would anticipate during this validation process and how you would propose to address them.

你作为一家大型投资银行的风险模型验证专家，你的团队负责对新开发的VaR引擎进行全面验证。该引擎旨在取代现有系统，并引入了更复杂的蒙特卡洛模拟方法和高维Copula函数来捕捉尾部风险和资产相关性。请你详细阐述你将如何设计并执行一套完整的验证流程，以确保这个新VaR引擎的准确性、稳定性、稳健性及符合监管要求。特别说明你会关注哪些关键点，可能遇到哪些挑战以及如何应对。