I recommend using Rogue Robe. First get to chapter 3 of the T.S.A.L. DLC.
Press QR QR QR E D. You will get some kind of spiky shield armour. Then go to the area that's almost at the beginning of the chapter. Go down the stairs to the left where the beam points. Press A S F which is Haste spell. I guess because the armour is spiky, the character is fast and the spell increases your speed simply touching creatures deals 2625 damage per touch. They have less hp than that so it's easy to kill them. They also spawn non-stop in that area. Ignore the big creature as you are only going to heal it if you touch it. Simply spam Haste, run through enemies and farm kills. If you get wet press F because if you try to cast the A S F spell you are only going to damage your armour as A is Lightning and you can't cast it while you're wet.

This is the first chapter of The Stars are Left DLC. An easy way to defeat this otherwise hard boss is to use (again) Rogue Robe and QR QR QR E D armor. After the spider is out go in front of the hole where it hides. Press D D D D D and hold left mouse button for a while. If you somehow hit Parker's head you can do up to 8k damage this way. When the spider hides in it's hole it's going to spawn 3 spiders (sometimes baby spiders too). What you want to do is press A S F and just run through them. Parker will go out again and you need to repeat the process. If you get caught in web press F to remove it. Note that if you set yourself on fire and extinguish it when your hp is down, you will need to press E to remove your current shield, wait for a while and then W to heal. Yea, you can't really increase your hp while you wear that spiky ice armor. Cast the QR QR QR E D spell again and repeat. Takes around 5 mins to kill the boss but it's a safe way.

This is the second chapter of The Stars are Left DLC. Yet again use the Rogue Robe and
QR QR QR E D + A S F combo. Just run close to the boss and you will defeat it in no time. Beware, it casts a spell that makes you move out of control, as well as one that can kill you
in 1 hit. I suggest to do some damage then move away, cast A S F again and repeat. Fairly
easy to kill the boss this way. I also got the no death on this level achievement as well using
this method.

First off, here's a page showing which enemies count as orcs - link[magicka.gamepedia.com]. You are going to need Dungeons and Daemons DLC and Party Robes DLC. I suggest doing it on normal difficulty because there are less and weaker enemies. Use the Rogue Robe as it gives you extra speed. Cast E D F which is fire & rock shield and simply run without killing anything. Takes about 2 mins per try and I got it on my first one, I think. Not a hard achievement. You may need some luck though as there's friendly fire and some orcs might get killed by trolls. When you go to the next area you are going to see a text notifying you that you've reached the Old Library. If the achievement doesn't pop up then restart the chapter and repeat until you get it.

Not my guide but thought I post it here - link[magicka.gamepedia.com].
You are going to need Dungeons & Daemons DLC. If the boss touches a spining saw it loses 14K hp. But for this achievement you can let this happen. So, as mentioned, you should use D QR QR QR QR and charge it. This way you can deal up to 9K damage. Not bad, right? Takes some time to kill this boss and if you don't use fire protection (either shield, or character that has fire resistance) this will be your wurst enemy. So make sure to keep E D F armor on you the whole time. Just don't stay too close to the spinning saws and keep charging ice rocks at the boss. Fairly easy achievement, imo. Took 2 tries or so.