Prepare for the pain.
Krogan Grunts start appearing as leaders at Force Level 6. Krogan Warriors appear at Force Level 11. Krogan Champions appear at Force Level 16. These enemies can only appear as leader of pods.
They use Advent Captain Rifles and their own fists.
Their capabilities per tier are:
Starting – Krogan Grunts contain immunities to poison, being stunned, and being panicked. They also regen +2 HP per turn.
Warriors – Krogan gain Fist Smash, letting them damage, shred armour, and potentially stun or knock out any enemy they hit with their fists. Has a three turn cooldown. They also gain the ability to smash through terrain.
Champions – Krogan gain React Smash, letting them use Fist Smash against any opponent that gets too close to them. They also gain Intimidate, giving them a chance to panic any enemy that uses a direct target attack against them.
They drop muton corpses because I am not even going try making another niche autopsy bonus.