To use Enchant Deadly poison on Assassin Cross you need an EDP/poison bottle which helps them to do maximum damage to the opponent/monster/Emperium.
For making a Poison bottle you need Create Deadly Poison skill on your Assassin Cross and following ingredients for the creation of the bottle:
- Berserk Potion x 1
- Empty Bottle x 1
- Venom Canine x 1
- Bee Sting x 1
- Cactus Needle x 1
- Karvodailnirol x 1
- Poison Spore x 1
The success of creating the poison bottle depends on your characters Dex and Luk stats. If you fail to create a bottle then you would lose 25% of your Max HP and you can even die if you run out of HP. Dex has more effect compared to Luk.
For better success rates Assassin Cross should use all kind of available buffs such as:
- Blessing and Gloria from a Priest or High Priest
- Dex and Luk Foods
- Poem of Bragi by a Bard or Clown to reduce the cast delay
- Marionette Control by a Clown on your Assassin Cross to increase its Stats
- Gospel from Paladin for addition stats
Equipment to be equipped during creation:
- Apple of Archer
- Slotted Coat or Jacket or Mantle or Valkyrie Armor with Poring card
- Knife  x 2 with Drops card x 8
- Morrigane’s Manteau (If possible)
- Crystal Pumps
- Gloves  x2 with Zerom card x2
The above are some basic equips suggested for low rates or servers with no custom equipment, but if your server have custom equips or can get better equips which are giving Dex and Luk stats then use them.
In case if I have forgot to mention anything then you can suggest via comments.