Here's a deck.   Fix it.  
It works ell against all types.  How could I make it work in modified format?  Thanks.

4 Grimer
3 Dark Muk
3 Murkrow
2 Cleffa
2 Magby

4 Professor Oak
3 Item Finder
2 Focus Band
1 Energy Charge
4 Computer Search
3 Gust of Wind
2 Nightly Garbage Run
1 Scoop Up
4 Super Energy Removal
3 Lass
2 Sprout Tower
1 Switch

12 Grass
4 Dark

Meta

I don't get it. In my career, until recently, I received a total of 2 deck fix requests. Now I suddenly have five people asking for fixes, two of which thought I was a Pojo staffer.

Ok, the Pokémon

4 Grimer
3 Dark Muk
3 Murkrow
2 Cleffa
2 Magby

This is fine, but drop the Magby for 2 more Cleffa. If you wanted to be original, you could try Dark Ariados. But Muk is the original.

4 Professor Oak
3 Item Finder
2 Focus Band
1 Energy Charge
4 Computer Search
3 Gust of Wind
2 Nightly Garbage Run
1 Scoop Up
4 Super Energy Removal
3 Lass
2 Sprout Tower
1 Switch

This is good for standard, but for Modified it is a whole different boat. For draw power there is Oak and Elm. For Search you use Breeder Feilds and Master Ball. Focus Band is a must. Maybe a few Boss's Way for the Muks. Nightly rulez in this format. Try some Rocket's Hideout.

And the Energy is fine.

Props to you Dragonmeta, the only work this deck needed was to be tweaked to Modified.

 

Shadow Assassin -The Dark, Mysterious Destroyer

I Do Deck Fixes