Link to the guide the video follows:
steamcommunity....
Below is basically a copy paste from the above guide.
First things first. To unlock dark world level 3-3 you need to create a 5-man tower anywhere on the normal map.
The level is pretty straight forward. A very strong and very mobile zombie and a dark sun that keeps on poisoning your units every other turn.
Minimum requirements:
- 1 Thief
- 7~9 Beast Tamers with bows
- 1 ranged unit that can kill your thief
Strategy:
1st turn (dark sun activates):
- Throw an unit close to the zombie and throw the zombie closer to the base panel.
- Send out a thief and use health on the zombie.
- Send other units out and throw the zombie on the island on the corner of the level. The zombie should be thrown on the panel closest to the main island.
- Don't send out your beast tamers so they don't get poisoned.
2nd turn:
- Send out all of your beast tamers (only 6 will be able to attack and avoid being attacked)
- Set up the other 3 so they get in their positions on the next turn.
- Combo the zombie. (should get 2 levels of bonus gauge)
3rd turn
- Set up the last 3 beast tamers and attack with everyone (should get bonus gauge to level 6)
4th turn
- Attack with everyone again and start to move back to the base panel (bonus gauge should be at 9)
5th turn
- Throw your thief at the island and use health on the zombie again.
- KILL the thief on with a ranged attack. If the zombie kills the thief with a normal attack it will regenerate and not die with the second poison.
6th turn
- Move out the units you want to level up (if there is a +xp reward).
- Stage Clear.
With this method you can easily and safely reach level 50+ very fast with all your characters.