Tainted Grail: Conquest

Difficulty set to easy
Use Zealot class
Get Quick Aim Passive
Reduce deck to 8 cards , 4 of which are Feints

The deck I used was 8 cards total
- arrows
aimed shot x1
smoke shot x1

- maneuvers
rancid battlefield x1
tails x1
feints x4

Win every fight by spamming Feints until either you use Ultimate, or Aimed Shot to kill a target in one shot.
Repeat as necessary

for this achievement spam rancid battlefield (-20 armor/ flip -30 Armor) on any enemy the weaker the enemy the easier the achievement. Repeat until achievement pops.

Guardian Kills -
for the Guardian fights in each area remove a card or grab a skill as needed.

don't grab any cards except for your deck, and remove cards as fast as you can before you grab as many skills as you can while getting XP and runes for armor and skills to help your feints. block ever hit with barrier from your feints.

I earned this by using the Blood Mage class, though the Summoner or Necromancer may also work. After getting to the end, instead of fighting the secret boss (if you took all 3 hearts), instead choose to fight the fourth guardian. On the way, be on the lookout for: in order of importance:

Death Mask - Every hit the enemy suffers also causes -20 Armour
Acid Saliva - Every hit from the minion causes -5 Armour
Acid Blood - Every hit from the minion causes Armour loss equal to minion level.

He has 4000HP, and the Wyrm will deal -3 Armour per strike, or 8 if you buff it with Acid Saliva, potentially up to 12 with Acid Blood and Acid Saliva. Combined with Death Mask, each Wyrm hit could potentially take away 32 Armour. As the Wyrm levels up, it will deal an extra hit per turn, so even without using any activations, over its normal lifespan it will deal -320 Armour. This means you need to activate it 7 times extra if you want to get it all in one Wyrm, assuming you started it at level 1 and applied all the relevant buffs and debuffs. If you need to, just summon and buff another Wyrm, or wait for the Death Mask card to be able to be used again. Death Mask is also triggered by any other attacks, so having an Abomination or two Wyrms at once greatly increases the chance of you being able to get to that -500 mark before the monster dies.

Using props to achieve goals is very simple. For example, using ACID FLASK 5 times on the same enemy in one round, you only need to pay attention to the timeliness of the props. You can also combine card effects with props.

During this time, you will also unlock