Grunt: Rite of Passage
This assumes that you have already explored Tuchanka, and have done the Mordin loyalty quest. If not, it is recommended that you familiarise yourself with the Mordin loyalty quest above, and the Tuchanka exploration section towards the end of this guide.
Speak to Grunt aboard the Normandy at it will be clear that there is something missing in his life. He has pent up aggression and is very tense. The logical step is to visit the Krogan planet of Tuchanka.
As soon as you touch down on Tuchanka, if you take Grunt along, a Krogan will comment on the fact that he has not yet taken the Rite. Speak to Urdnot Wrex or Wreav to get his view, and he will agree that Grunt must take the Rite. Not everyone has this point of view, however, and Urdnot's rival, Uvenk, is your main adversary at this stage. However, Urdnot makes it clear that you have his permission to continue, and allows you to speak to the Shaman upstairs to begin the Rite.
While speaking to the Shaman and Uvenk, use the Renegade interrupt if you want to assert your dominance in this case. Eventually, Unvenk will slink off and you can accept the duty of being Grunt's krantt, and assisting him in the arena battles that make up the Rite. Confirm that you wish to begin.
Speak to the Shaman with Grunt and agree to take the Rite with your squadmate.
As Grunt is with you, the soldier category is covered, and you will want a biotic with you to deal with the early rounds of the Rite. Pick the second character based on whatever you won't be able to cover with your main character.
Survive the Rite:
You will find yourself in an arena. There are many ammo, power and medical stashes to collect once the rounds begin, as well as a crate of Refined Platinum and parts to salvage behind the keystone. You may want to save some ammo and health for the third round of the Rite, though more ammo will be dropped along the way. Be sure to plunder any corpses you come across in the arena, too.
The first wave contains Varren. Activate it by interacting with the green keystone. You should be adept at dealing with these critters by now. Stand back from the slopes leading down to the lower level to give you plenty of time to line up shots and take out the creatures before they get too close. Use biotic attacks as a fall-back should you get overrun. Concussive Shots are good to render the Varren helpless to further attacks, too.
Use your tried-and-tested tactics to combat the Varren.
With the first wave down, collect any ammunition and med-kits you need before returning to the keystone. Activate it again to begin the next wave.
The second wave contains Klixen. You will have experienced these if you have done Mordin's loyalty quest, but if not, they explode when close to your team and on death. As with the Varren then, the key is to take them out from range. The only risk is the splash damage that may reduce your shields once you destroy each Klixen. Just be sure to strafe out of their way wherever possible, keep an eye on your team's position in relation to the Klixen (remember that you can direct them around the arena using the D-pad [Xbox 360]) and use biotic and stun attacks like Concussive Shot to keep the beasts at bay.
At the end of the round be sure to let your shield recharge and stock up on ammo. You'll need full supplies of heavy weapon and your favourite other weapon ammo for this intense final fight.
Activate the final wave.
The third and final wave contains a Thresher Maw. This emerges from the ground to the right, centre and left as you look out of the arena into the distance. At first just its tendril shows. Resist the urge to waste ammo on it, and wait until the full crab-like enemy is in view. As soon as it is, use heavy weapons. You should be able to see when it is readying a shot, and at this point you should ensure a pillar is in between you and the Maw. Don't cover behind a pillar, because the Maw will just destroy your cover. You should be able to strafe behind a pillar and use it as an object between you and the enemy to block its shots, without those shots destroying it (see video).
Once it has fired some shots it will dive back underground and appear in one of the two other locations. You should be able to spot where it is going to appear by the debris cloud that follows it underground. Be ready with your weapons to inflict damage. A sniper rifle is a good high powered option, but when scoped you cannot see the Maw readying its attacks so easily.
Keep a pillar between you and the Thresher Maw when it readies its main attack.
You must beware of its powerful rocket attack. This will destroy your shield even if it misses you by some distance. About three hits without considerable time to recharge health and shields will kill Shepard on Normal difficulty. As soon as your shields are down, seek cover, and if you get to the bloodshot stage, run away and let your team take the heat temporarily!
Note that you do not have to kill the Maw. The objective is merely to survive five minutes in the ring with it. If you are really struggling, therefore, just try to spot which side it is appearing at, and then hide using the walls of the upper level for impenetrable cover, but which you cannot reasonably fire back from. There is kudos to be had, both from the Krogans back in the town and in an achievement (Big Game Hunter - 10G) for killing the Thresher Maw, as opposed to merely surviving.
Take pride if you defeated the Maw, surviving is achievement enough
If you thought that would be the end of this quest, then think again. Right on cue, Uvenk turns up, professing admiration for Grunt's skill in battle. It is clear that he is not being sincere, however, and Uvenk and his Krogan henchmen engage your squad in combat. This is easy compared to the Thresher Maw. As with fighting all Krogan, attack the nearest one first as they are deadly in close-quarters. Use a sniper rifle if availablee, to take down their defences and allow your biotic team member (or yourself) to finish the job. Thankfully, there is plenty of cover available, and you should find this battle relatively straightforward.
With Uvenk defeated, the Shaman returns to congratulate the newest member of the Urdnot clan. Grunt honours you as his battle-master, tying him to you in a clear profession of loyalty ahead of your great trials to come.