Sapper (Marine) Guide

Role
The Sapper acts as the team's mobile defense. The Sapper, with its gun, grenade, and stim, has the highest damage output of all the miner heroes. For this reason, a Sapper is crucial in providing defenses early on from Zerg heroes while the rest of the team build static defenses. While the Sapper cannot attack rocks with their hero, the mining charges more than compensates for this. Additionally the mine layers the sapper provides are immensely valuable for the team's overall defense

Skill Points and Items
As sapper, the skill order is:

9 Engineering -> 1 Weapon -> 3 Defense -> 10 Offense.

The 9 Engineering is to upgrade your gun to level 3. The 1 weapon is to be able to build an Engineering Bay to buy a gun. The 3 Defense to be able to build minelayers. The 10 Offense is more damage against tankier zerg heroes

The ideal setup for items would be: level 3 Gun, level 3 Armor, and level 3 Marching generator and level 3 Geoskanker. You could substitute a level 3 protoss shield instead of armor. Also try to keep a shock grenade on you at all times as you should be the one fighting zerg heroes the most.

Strategy
Early game, you are probably the fastest miner, so spam those mining charges whenever possible to give your team XP. As your team won't be situated for some time, protect your allies against any zerg units that come. Once your team's bases are set up, start making a barracks to train miners for income. Suppliment your team's defenses with minelayers. Upgrading minelayers are not necessary as the level 1 variant is good enough.

With your barracks, train marines, marauder, and medics as a mobile defense with some bunkers and look for anywhere your teammates need help. If you need supply, either upgrade your barracks or find some terrazine. This means you should be responsible for clearing out creep tumors, ziggers, and chasing zerg heroes away.