In one of the most explosive crossovers in Marvel Comics history, Iron Man and the Avengers battled the Transformers' Megatron and his army as they tried to take over Earth. Tony Stark developed his own Anti-Transformer armor to combat the Decepticon, specifically made to take on the powerful transforming robots. However, Megatron's power proved too much for the hero's new armor, destroying it quickly.
New Avengers/Transformers from Marvel Comics and IDW was a crossover that brought Earth's Mightiest Heroes and the Transformers together. The four-issue miniseries by Stuart Moore, Tyler Kirkham, Sal Regla, Anette Kwok, and Todd Klein featured the Decepticons launching an attack on Earth, using an Array to saturate Latveria and Kymkaria with mind-controlling radiation. In doing so, the Decepticons (led by Megatron) wanted to start a war on Earth to strip the planet of Energon fuel. The Decepticons even powered themselves up with Spider-Man's blood, leading Iron Man to use his own secret weapon alongside the Autobots: His Anti-Transformer armor.
In New Avengers/Transformers #3, Iron Man reveals to the Avengers he's been expecting an attack like the one from Megatron and the Decepticons. Optimus Prime asks Tony Stark what his Transformer-sized armor is made from, as the hero reveals it's made from carbon nanotube transistors, printed on silicon wafers, with a capacity of about fifteen amperes. Optimus agrees the suit should be sufficient in battle. However, Iron Man quickly notes there's a major flaw in his Anti-Transformers armor. While battling Megatron, the power levels in his suits fluctuate considerably, as Stark admits the suit is a massive power drain. As a result, Iron Man doesn't fare well in a one-on-one fight with Megatron.
After the giant-sized Anti-Transformer suit gets a couple of blows towards Megatron, the Decepticon leader cracks the armor with a powerful punch - leading to Iron Man's armor to emergency shut down. Tony Stark reveals he still hasn't worked "the kinks out of this model yet." Megatron proceeds to decapitate the armor with a powerful blast of energy.
While the Avengers and Autobots would eventually find a way to defeat Megatron and the Decepticons, Iron Man's Anti-Transformer armor failed spectacularly. Clearly, it wasn't ready to take on a threat as big as Megatron, leading to its destruction. Still, seeing the massive Ant-Transformer armor in action against Megatron is quite a sight to behold. However, Iron Man will need to make a few upgrades to the suit if he plans on ever taking on Megatron in a rematch.