There are two scenarios.

1. Ral Zarek uses his knowledge of planeswalking to create a portal to middle earth. He convinces the great firemind, Niv-Mizzet, to send a team of ten Izzet scientists with as much equipment as they can carry. Once in middle earth, Ral Zarek wants to delve into the mineral deposits of middle earth to learn more about topography and the worlds mineral composition. But why mine when the Dwarves of Middle Earth already did so. However, Ral Zarek and his buddies encounter a small problem, Smaug, the scourge of Middle Earth. Can Ral-Zarek outsmart the dragon with a team of Izzet scientists?

2. In an alternate reality, Ral Zarek opens the portal but gets invited by Vorel of the Simic guild to a party in New Prahv. Ral Zarek gathers up all his buddies for a night of partying and drunk science with the Simic guild in New Prhav, leaving the great firemind Niv-Mizzet to look after the guild's hearth. While most of the guild is out partying, Smaug finds his way into Ravnica through Ral Zarek's portal and wishes to clash with the firemind for all the great treasures held by the guild. However, Niv-Mizzet, being a dragon, won't give up his treasure without a fight. Atop the skies of the glorious city of Ravnica, Niv-Mizzet and Smaug clash for dominance. Who would win?

Smaug is a well know character but for those who want a bit more clarification on Niv-Mizzet and the Izzet I refer them to this;

http://wiki.mtgsalvation.com/article/Niv-Mizzet

http://wiki.mtgsalvation.com/article/Izzet_League

However, despite Niv-Mizzet's vast knowledge, Smaug is no pushover as he was able to defeat the entire mountainhome of the dwarf civilization of Erebor;

http://lotr.wikia.com/wiki/Smaug

Who would win?