Diamond Lion from Modern Horizons 2 is another awesome callback to a Legacy staple, in this case Lion's Eye Diamond.
If we're doing a direct comparison, Diamond Lion is obviously much weaker since it comes down way slower and suffers from summoning sickness. However, Modern is a much weaker format than Legacy and Lion's Eye Diamond is one of the most powerful cards in the game. So let's still take a look to see what it can do in Modern!
The Echo of Eons combo deck that is played in Legacy could potentially be ported to Modern using Diamond Lion. This deck aims to have either of Narset, Parter of Veils, Hullbreacher, or Notion Thief in play before casting Echo of Eons. This actually curves neatly with Diamond Lion, letting you case one of the three mana options on turn 3 and then using Diamond Lion to flash back Echo of Eons.