Anime

The first Mechtogan Titan appearance in the anime was in Chaos Control, where it showed Razen Titan. He was standing behind Razenoid and Mag  Mel absorbing Chaos Energy.
In Triple Threat, Dan Kuso, Titanium Dragonoid and Zenthon joined together and put themselves in perfect sync to summon Zenthon Titan. At the end Zenthon Titan defeated all of Sellon's Mechtogan.
In Battle Lines, Dan, Drago and Zenthon summoned Zenthon Titan in order to help them defeat the Chaos Bakugan and the Mechtogan.
In Unfinished Business, Drago and Zenthon summoned Zenthon Titan in order to help fight against Venexus Titan.
In Behind the Mask, Dan, Drago, and Zenthon summoned Zenthon Titan in order to help fight against Mag Mel, Razenoid, Dreadeon, and Razen Titan.
In Dark Moon, Shun summons Faser Titan, Dan summons Zenthon Titan and there are many Razen Titans.
In The Final Takedown, Zenthon and Zenthon Titan used the rest of their strength to obliterate Dreadeon and Razen Titan, which also cost them their lives.