While Blaziken got an instant boost (no pun intended) and went off on a meteoric rise to Ubers, it's not the mon that impacted the game the most. The answer to the question "What Pokemon has most significantly changed the game because of its DW ability?" is undeniably Drizzle Politoed. It brought the universally present Rain into OU, ended up getting Swift Swim users banned when used with him, and boosts the power of a whole host of things, and the accuracy of more. Tornadus-T, Thundurus-I, Keldeo, Scizor, Ferrothorn, Genesect... all of these benefit hugely from the Rain and have been in the top threats to prepare for since their release. Drizzle is THE most broken ability in the game, and there's a reason Kyogre and Groudon are in Ubers.
And to those that think that auto-weather isn't the reason, we brought them down to OU in Gen 4 (de-leveled to 70 to roughly match average OU power at the time) and then they immediately got banned because of Drought and Drizzle.
Politoed is the most ridiculous force in the metagame right now. Zero to hero indeed.