Dungeons 3

This is done in the "Two Sides Of A Medal" level. A very tight time-based trophy requiring you to build quickly and get to the Overworld as soon as you can. It won't be easy but definitely doable once you know where to go and what to do. The 2 Obelisks can be found in the following image:

Follow the path shown above to find the 2 Obelisks quickly. In terms of timing, you'll need to have found and captured the 1st Obelisk within 10 minutes or under, then push towards the 2nd by the 15th minute, finally getting close by the 20th minute. The 1st captured Obelisk and its attack will help greatly in this task and so will Meteor Shower and Demon Strength. Focus on Horde creatures for this trophy as they are quicker to hire 7 creatures which is the max before you need Evilness. Make sure to aim for Hero healers and spellcasters before the rogues and archers. You also need to factor in 90 seconds of corruption time per Obelisk for the trophy to count, you can't just "find" them.

Once you've successfully corrupted the 2nd Obelisk in under 25 minutes the trophy will pop.