With double buffs on, Ezreal might as well be a different champion.
With the Red buff inflicting a Slow effect and True Damage, and the Blue buff reducing skill cooldowns and replenishing mana, Ezreal was able to use his skills to much greater effect than normal.
For instance, regarding the most crucial kiting skill, Arcane Shift:
At the highest skill tier, Arcane Shift had a base cooldown time of eleven seconds. The maximum cooldown reduction you could get was up to 40%, which was how much he had now, meaning his Arcane Shift had an actual cooldown time of about seven seconds. Every 1.4 seconds, hitting something with Mystic Shot would reduce all other skill cooldowns by one second. That meant Arcane Shift could be used every four to five seconds!
Being able to emulate Flash every four to five seconds, in addition to an actual Flash spell for emergencies… who could hope to pin down a fleeting phantom like him?