One card in particular that I think could use another look is Patron of the Moon: (EDHREC Rank: #620) While the card is expensive, its Moonfolk offering ability allows you to discount the mana cost by sacrificing a Moonfolk, and you can cast it an instant speed
It's the same thing, every game
This includes weekly League nights, the upcoming Set Championships, and Challenge/Worlds events
The most efficient of these new Hydra-like creatures is Mawloc, who fights opponent creatures when they enter the battlefield, and even comes at a base 2/2 before paying any X costs
There are some clear, high-value cards you might have heard of Mana Reflection, Dryad of the Ilysian Grove, and Dark Depths
The Lost Caverns of Ixalan, Magic: The Gathering's latest foray into the bombastic and the swashbuckling, understands this idea better than most