u/MariaMagdalenaXXX

Requirements: Have the first seven cards in hand and draw an untapped blue source in your first or second draw step

1. T1, play [[Ancient Tomb]], tap to play [[Grim Monolith]], pass and hope your opponents put some permanents on the battlefield
2. T2, play an untapped blue source and tap all your permanents for mana, giving you 5U
3. Play [[Urn of Godfire]] and activate its first ability once for U, giving you 2UU
4. Enchant your Grim Monolith with [[Power Artifact]] using UU and untap it with the remaining 2. Boom! Infinite mana of any colour
5. Play [[Tourach's Chant]]
6. Play [[Doppelgang]]. Unfortunately, it needs at least X distinct targets and you only have 5 permanents in play. But, perhaps you have one opponent and they played two lands and a creature, bringing the total to 8. So you can cast Doppelgang X=8, giving you 9 copies of Tourach's Chant. You can also throw in [[Eternal Witness]] to loop back the Doppelgang, but that then requires you to draw your blue source T1
7. Play [[Explore]], drawing [[Yavimaya, Cradle of Growth]] and play it

Now, anyone who plays a land will get hit for 27, only being able to lower this somewhat when they send whatever creatures they have to the yard. This includes you, but luckily you have infinite mana anyway :)

Edit: I completely missed that this only works in Commander as you'll dome yourself for 27 by playing Yavimaya. Thanks for the catch u/heretolurk613!

Edit 2: It does not seem to be so easy after all. As per u/Ansixilus' comment, a continuous effect like that of Yavimaya can only be generated by an object on the battlefield, so the effect seems to be technically not present yet at the time Yavimaya enters?

Edit 3: It seems to trigger after all https://www.reddit.com/r/mtgrules/comments/1vpuht9/question_about_continuous_effect_timing_rules_and/ (per rule 611.3)