Ghostbusters

Update: @Sashamorning - you can connect controllers at an end of a level to upgrade the other characters. "I found Sparky's Remix to be a bit faster. I got around 340,000 in 20 minutes. Otherwise, I was averaging around 10k/minute per mission. I also found it fastest to use the minigun, use the perk to fire it faster, and blow up everything in sight."

When you've connected the controllers, pause the game to "Join Game".

2-4 controllers method:

If you have 4 controllers then this ain't gonna take long at all. (unfortunately I didn't know about this so I did the long method).

Since this game is local only, you can save a tonne of time if you have 4 controllers. This way you can upgrade 2-4 characters once you've finished a level, whereas if you're playing with one controller you can only upgrade the selected character.

- Fully upgrading each character is getting to level 30.
- Ecto is what's required to level up.
- Remember to connect the controllers in at an end of the level (Preferably when you're about to trap the last ghost).
- Try to get x10's when ghost trapping for ecto.
- Try to find all the hidden areas for ecto.

Tip - you can detonate a grenade by pressing LT again.

If you only have 1 controller:

When you fully upgrade one character and move on to the next, make sure you downgrade the fully upgraded characters before starting a new one. So lower their weapon power, weapon range, etc.
This will mean the AI won't be able to defeat the enemies that easily, making you receive most of the ecto.
Also make sure your weapon power, ghost traps and ghost trap rewards are maxed out to gain much ecto as possible.

To unlock the achievement make sure after, that you upgrade them all back to max stats - so 5 for everything.

Please let me know if I can add anything else.