The Colossal Titan is pretty powerful figure that scared the entire planet, but the heroes didn’t have an Omnimon to help them. Omnimon has a powerful blade and it would work pretty well against a titan. A single strike should be enough to take the Colossal Titan out of the fight and Omnimon also has enough speed to dodge any possible counters. No amount of regeneration can save the Colossal Titan! Greymon wins.
Link to the original image by Vizar-Aizen can be found below.