For example, the Mim Bounce Package (Madame Mim - Snake, Madame Mim - Fox) can combine with any of the characters above to reset them, allowing you to retrigger their when played abilities
Nethergoyf Nethergoyf isn't seeing a ton of play in Modern just yet, but it's playing hand-in-hand with Psychic Frog in Legacy, where it seems to be playing the new role of Delver of Secrets in low cost decks that want to easily put a bunch of cards into the graveyard
Teferi himself can't win a game at all so you really want other walkers to go with it
There is also an emphasis on casting larger spells to trigger beneficial effects
Plus, for a rundown of all the cards across the set and where you can find them, check out the Collecting Dominaria United article, which includes details on the Lost Legends cards
Cost reduction comes in the form of mana dorks like Zhur-Taa Druid and Ruby, Daring Tracker, but also cards like Goblin Anarchomancer