The Payoff
"Lethal direct damage equal to Phyrexian Devourer's (huge) power"
Requirements
Goblin Welder
Phyrexian Devourer
Fling
The Combo: Storyboard
Step 1
Get Phyrexian Devourer onto the battlefield. Goblin Welder can weld it in from the graveyard, sacrificing a spare artifact, so it never has to be hard-cast.
Step 2
Activate Phyrexian Devourer, exiling cards from the top of your library to pile on +1/+1 counters. Hold priority while its sacrifice trigger (power 7+) is on the stack.
Step 3
In response, cast Fling sacrificing Phyrexian Devourer, dealing damage to the opponent equal to its now-enormous power.
Step 4
The opponent takes lethal damage in a single shot.
⚠ Rules Note
Phyrexian Devourer's triggered ability sacrifices it once its power reaches 7 or greater, so Fling must sacrifice it (or be cast with that trigger on the stack) before it dies on its own. Fling deals damage equal to the power as last seen. The damage ceiling is the total CMC of the cards exiled from your library, which is almost always far more than lethal.