For the best performance and security, it is recommended to use the official App Store :

: A modern 3D reimagining with Roguelike adventures and real-time PvP.

‎METAL SLUG 3 App - App Store. METAL SLUG 3. Action. $2.99. METAL SLUG Pack - App Store - Apple Compatible with iPhone, iPad, and iPod touch. Metal Slug: Awakening - App Store

If you are looking for specific older versions or delisted titles like Metal Slug Touch , these are often hosted on the Internet Archive for historical preservation: Metal Slug 3 - App Store