In an alleyway skirmish, using terrain to gain the upper hand can be accomplished through several strategies: 1. **High Ground Advantage**: If there are any high ground or building roofs in the alleyway, try to occupy these high points to gain a view and shooting advantage. 2. **Obstacle Cover**: Use obstacles in the alleyway, such as walls, boxes, cars, etc., to cover yourself while observing the enemy's movements. Make sure to move behind cover to reduce the time you are exposed. 3. **Flanking**: In an alleyway, a head-on confrontation may be dangerous, so try to flank the enemy by moving through the side alleyway or building to launch a surprise attack. 4. **Take advantage of narrow spaces**: The narrow nature of alleys makes it difficult for the enemy to launch a large-scale attack, so you can use this to your advantage to launch a quick raid or retreat. 5. **Planned Movement**: When moving in an alleyway, you should keep a low profile, move quickly, and always pay attention to what is behind you. You can choose to quickly move through the alleyway to reach your target location before the enemy can react. 6. **Control sight and sound**: Use the winding characteristics of the alley to reduce your visibility and sound, keep quiet, so as to grasp the enemy's position at any time. 7. **Set traps**: If conditions permit, set obstacles or baits where the enemy may pass, so that the enemy will be passive in action. Through these strategies, you can effectively use the terrain of the alley to gain the upper hand and increase your chances of survival and victory.