Lara Croft and the Temple of Osiris

To kill Khepri and complete all of the Challenges for the Tomb you need to avoid his fissures which are the glowing circles on the Meteor and in the second part of the fight avoid all his Meteors which he launches at you. The final Challenge is to defeat him in under 5 minutes which is very easy if you use the Shotgun.
When the fight starts place bombs with next to his claws and detonate them again using he will then raise up exposing a yellow circle on his chest which you can shoot with your shotgun, if you have a weapon damage ring on he will lose health really quickly and you'll be on to the second part of the fight. Continue to plant bombs and shoot him till the ball moves.
For the fissures just avoid them at all costs if you want the Challenge Achievement.
When the second part of the fight starts he'll be throwing Meteors at you and these are easily avoided by simply stepping backwards other then that and a few Scarabs its the same as the first part.
If you avoid all the fissures and Meteors you'll net 2 Achievements in this fight.

Here's a video showing how to do it.

Okay okay for this achievement you must end this ugly bugs life. Once you get to him... ( main story ) you'll be placed on a moving fiery rock that you must fight him on while its moving, you'll have to avoid the fire and his simple basic attacks blah blah it's real simple. When his hands Glow yellow place Lara's bombs with the button and then again to blow those bad boys up.

Everytime you blow up one of his hands the creature cocks back and allows you to shoot him where it is glowing on his chest ( can't miss it ) I suggest thee shotgun or m16 as they are thee most powerful so far. This part should only take you about 10 minutes no less.

Good luck to all on the quest !!!! Message for Help

I've created a two-part 100% walkthrough video. It covers every single achievement in the game except the co-op ones and the speedruns, but the co-op are self-explanatory and the speedruns are super easy once you've played a level, since you can usually just run past everything and solve the puzzles most of the time. Contrary to some reports, you CAN get the gold points challenge on EVERY tomb on your first time through in solo play. Follow along with the video below as you play through the game (and part 2) to have your 1k in 8-10 hours tops. A detailed text guide follows after the time stamps for those that prefer it, copied over from the walkthrough I've written for this game.

This achievement is story-related for finishing the Tomb of Khepri.



Timestamps:
00:07 - Pyramid of Osiris
13:32 - Tomb of the Timekeeper
22:08 - Challenge Tomb #1
25:00 - Tomb of the Silversmith
35:42 - Challenge Tomb #2 (west/southwest from Tomb of the Silversmith)
37:55 - Khepri's Tomb
42:52 - Oracle of Osiris
46:50 - Challenge Tomb #3
49:50 - Tomb of the Ferryman
1:02:22 - Challenge Tomb #4

Challenges: Defeat Khepri in under 5:00; Dodge all falling meteors; Dodge all of the lava fissures on Khepri’s ball

Khepri’s tomb is accessible after you’ve completed the Tomb of the Silversmith, and is required for its piece of Osiris to complete the main story. I don’t know if the game specifically directs you here later on, but I wandered over to it at this point so I’m placing it here as the earliest opportunity, as far as I know, to complete it. There are only three challenges for this, as it is essentially just a boss fight rather than a fully-fledged tomb.

You should have found an assault rifle by now in one of the first couple of tombs, and it makes quick work of him. The falling meteors will make an orange circle showing their impact, so make sure not to be standing near them when they fall. Lava fissures are the circular pits of fire on the ball. If you get damaged by a fissure or meteor, just pause and restart the tomb. To open his weak spot, place a bomb by one of his claws and detonate it, then unload on his chest with your rifle. The fight has three phases, with scarabs showing up part way through to add to the chaos, but it’s a relatively simple fight. If you’re using the assault rifle on his weak spot you should finish the fight in under 5:00 easily, and assuming you got the other two challenges you will net both of his achievements in one go.