Basically, you only need the tool: Lag7.
It is usefull for many other achievements, but in this case i only needed it for "In the Hall of the Mountain King" and "One Step at a Time".
How it works:
For: In the Hall of the Mountain King
Get Lag7 and set it to 7 seconds delay. If you use speed boosts in wow which last 5 seconds and you use the Lag7 at the last seconds of the speed boost, you will lag for 7 seconds and you will still have the speed buff for the entire time. In this case you use speed buffs right after entering the Hall of the Mountain King and you can basically rush to the next door in 5 seconds.If you use Lag7, you wont trigger any traps or mobs, so you will reach the 2nd room without adding any mobs or getting dmg. In the second room you will start to loot big chests, like 3-4. One chest will spawn a mob, if you kill him, and loot him you will complete one part of the achievment automatically. After the second room, you will have your speed boost again. Time for Lag7! you can choose where you want to use it. I prefer after to use it if after i opened the 3rd door (left side) and rush to the right side and the boss. You will almost reach the boss all the time. there are almost 4-5 big chests and you will have enough time to loot them. left to the boss is an npc, you have to take his speak option and the scenario will end earlier. you will have completed 3/4 parts of the achievement very easy and if you're lucky you got 10 chests. you will have 7-8 chests very easy and you only have to search for a few more. time should not be a problem.
For: One Step at a Time
This Achievment consists of 2 parts. Both are dailies and not up at the same time, but still available. in order to have sucess you must not take any dmg during accepting and turning in the quest. (so after killed a boss i recommend hearthstone to get out). the mobs are located in a hall without any entrance door, but doors inside. What you will do: get on flying mount outside the hall and start lag7. you can basically fly the whole way to the boss without tagging or pulling anything. you will skip atleast 50% of the way. after the lag is over you have to make sure you dont take falling dmg. the hall is full of mobs and traps, but they wont be triggerd if you use lag7, so it should be really easy. for milau is another hint: when he wants to pull you, go next to the fence on his platform and he will pull you against the fence and not through the whole room.
important: lag7 can make you disconnect, so dont spam it and dont spam it after one lag is over. i recommend doing some tests outside before using it.
what's really happening: if you're standing at a spot "A" and you press lag7 and start running trough a room to spot "B", the server will think you're still at spot "A". (anything between(mobs trapps) is skipped). after the lag you're position is updated to spot "B".
make sure, that spot "A" is save!!! if spot "A" makes you pull a mob, because the mob comes to close to spot A, he will run to spot B.
my english op