Ultimate Crit Build for Iggy and Scorch

Summary (TLDR)

The key to this build is it's 56% Crit chance. Iggy's abilities are focused on damage over time (DOT), and this presents a lot of opportunities for crits. Focus on crit cards and then energy damage, and overwhelm your foes with flame towers.

Abilities Overview

Main focus is on Flame turrets. Block lanes and hold the line.

Your basic attack, Molotov, will do decent damage by late game, but does no DOT without other Oil Spill/Slick, so be sure to use abilities before running using Molotovs

Use Oil Slick to get behind enemies to use Flame Belch or as a panic move to leave a fight when necessary.

Oil spill is okay, but its cooldown time and relatively short DOT. 

Use Flame Belch to finish off enemies or, in some cases, to save your life in tough situations where there is no clear escape.

Abilities upgrade priority

Priority in order:

-Flame Turret

-Flame Belch

-Molotov

-Oil Slick

-Oil Spill

Abilities Combos

When you encounter enemies, use Oil slick to quickly retreat while leaving an oily path that can be ignited by placing a few Flame turrets. Then, back up and start throwing Molotovs. Finally, use Flame belch to finish off enemy players. 

Card Build

The above cards are a recommended set based on what I currently have available. If there are passives you don't have, simply replace it with any available passive with Crit chance or energy damage. Likewise, if you are missing any of the above upgrade cards, replace them with any available Crit chance or energy damage upgrade cards.  

Jungling

Although capable of jungling this build tears through enemy minions so quickly that it likely isn't worthwhile to waste your time. Rather, if passing through the jungle, be sure to stop by the Harvester with whichever Harvester key you have equipped. 

Laning

This build is the master of holding lanes. Simply throw down a few flame turrets and watch as the enemy is not only halted, but very quickly burned to death.

Ganking

Although running down enemy players is an option, it is probably best to simply finish them off with flame belch when the option arises. Again, focus on Laning with your Flame turrets.

Conclusion 

To wrap it up, for cards, focus on crit chance and energy damage, While in game, focus on laning with your Flame turret and racking up minion kills while pushing the front forward for your team.