Sniper: Ghost Warrior 2

need an easy way to take a little bit of damage with no risk? stay underwater for a second too long on the first level, takes half a 'block' of health which counts as taking damage

The very first mission is probably the easiest one. You can die as much as you want. Just never use the medkit obviously. You can play on the easiest difficulty if you want, but the mission is supposed to be stealth anyway so this is easily done on any difficulty.

You can do this most efficiently on any mission where there is water that you can swim in, which is just about all of them.

First of all, and most obviously, do not use a medkit at any time during the mission.

Swim under water and stay there until the bar on the right indicating your breath meter is fully depleted. When you start taking damage from drowning, then resurface. This will count as taking damage.

Now go ahead and complete the mission. Note that you can die as many times as you like, but if you die and restart at the last checkpoint you will need to go back underwater and damage yourself again. Once you have taken the damage, you need to then complete the mission without dying or using a medkit.