Legend of Valhalla achievement in Thor: God of Thunder
Start by playing through the game on normal. Focus on getting all the other achievements as well as all the collectibles that you can. Make sure as well to do all the feats on every level as well. On Valhallan Difficulty these can be near impossible. Just do your best to leave yourself with nothing but (Hard Mode Only) collectibles and beating the game on Valhallan difficulty, otherwise you're going to have a bad time.
In a Valhallan Difficulty play through, cheap tactics are your bread and butter. Throw enemies off ledges for instant kills, pound them while they are prone, and in general refuse to give a target a single inch once you pick your prey. You will also have the advantage of knowing each level and only needing to use a collectible guide to find the rest of the power-ups only available on hard mode.
Three problem areas I encountered were:
*Spoilers Ahead*
1) When you first release Mangog and are fighting Laufey, Make sure to stay as near the rune as you can. As soon as Laufey is dispersed get on the rune and power it up. I had trouble maintaining my health through three encounters with the Ice Giant King. So instead I was able to power up the rune in only two encounters by sticking close to it. This will still probably take you several tries to get the timing down to be next to the rune when he disperses as well as knowing the exact instant he is going to disperse so you can start running towards the rune before he disappears. If you feel you can avoid Laufey's attacks for the most part you can consider playing "chicken" with him and continue charging the rune after he reappears to get every microsecond out of it you can.
2) The final bosses for Muspelheim and Vanir each are difficult to stun and make susceptible to a contextual button barrage. Use the Buzzsaw throw. Simply lock on to your target, hold down left trigger and hit x while at a distance. If you did it right mjolnir will spin horizontally towards your target while crackling electricity and stun them. This allows you to get in close for one or two hits then jump back and rinse and repeat, activating the button presses when you can to remove large chunks of the bosses life. Patience is the key here. Getting greedy and attempting to defeat them quickly will result in repeated attempts.
3) Mangog. I hate Mangog. This will be the hair pulling part of the game. You'll need to knock down Mangog's life bar three times.
Phase 1 isn't too difficult but if you get hit more than twice you may want to let yourself die and restart. You need to damage Mangog enough to start the button pressing sequence. You will need to run through this sequence three times.
Phase 2, he shoots homing fireballs at you. If you can time it, it is much easier to hit the projectiles back at him rather than trying to dodge them. Dodge his leaping attack then shoot in to begin the button pressing sequence. Do this three times.
Phase 3, congratulations you made it this far. Nothing feels worse than failing here. You need to fill your odinforce completely to stun Mangog. Instead of the typical lightning barrage, it calls Loki. Loki distracts Mangog for a VERY short period. During this small window you need to get close enough to activate the button executions flawlessly. Once again rinse and repeat three times total.
Once you finish the last phase jump up, spike your controller, and scream victorious curses.
*Remember if you feel frustrated and your patience is waning you will tend to make mistakes easier and rush boss battles you shouldn't. Take a break and walk away or do something else for a few hours before coming back. Doing that will reset your patience and you'll be able to reattempt whatever is giving you trouble more methodically.*
