The reason that people are not playing with Heros Downfall as much as they probably should be is that the 1BB mana cost is extremely taxing on a mana base that also wants to have 2UU for Jace, Architect and 1UWW for Supreme Verdict on turn 4
Commander Masters Spoilers July 17 | Preconstructed Commander Cards Commander Masters Commander Decklists Commander Masters Spoilers July 18 | Superfriends Support Commander Masters Spoilers July 19 | Enduring Enchantments New Cards Commander Masters Spoilers July 20 | Eldrazi Support
This means that Commanders, mana rocks, and other legendary permanents arent going to be affected by Desynchronization
There are a few other notable cards that might affect Modern, such as Wayward Guide-Beast - a hasty 2/2 with some interesting land return ability - and Magmatic Channeler, a card that not only draws you cards but gets larger as they enter your graveyard
Some of my other favorites are Reliquary Tower, Rogues Passage, Maze of Ith, Scavenger Grounds, etc
The blue-green specific part of the triad is the most ramp-centric