This combo takes down enemies in a massive one-two punch.As a krogan, Grunt's endurance in combat is unmatched.Loyalty unlocks a fourth usable power (which can be taught to Shepard as well using the appropriate research option) and an alternate outfit.Loyalty also plays a major role in determining character survival during the Suicide Mission. Certain upgrades affect only Shepard, certain upgrades affect only a specific squad member, and some affect the whole squad. Your intended play strategy and preferred squad will affect which upgrades are most important to research and which ones can be skipped.Another option is to wait until the current firefight is resolved, at which point the fallen character(s) will automatically revive.Squad members have effectively unlimited ammunition reserves and do not need to pick up clips, but they suffer both a damage penalty when using weapons, as well as an increased cool-down on most powers when compared to Shepard.After his loyalty mission he gains an ammo power, Armor Piercing Ammo, which inflicts significant additional damage against armored and unprotected enemies.
If the mission in question is a character's loyalty mission, then that character must be in Shepard's shore party.
If you'd rather take shields down with weapons fire than Overload, you may want to consider Zaeed as a replacement for Garrus since they carry the same weapons and Zaeed boasts greater damage output along with Disruptor Ammo.
Another great pairing is Garrus using Overload on a shielded enemy, then immediately following up with an Incinerate from Mordin Solus.
Otherwise, the player is free to select any characters which have been acquired.
Squad members can be given orders (move to position or attack target).Along with his unlockable Fortification ability, this makes him very hard to kill.