The goal for Echo of Eons is to put it straight into the garbage can, preferably with Lion's Eye Diamond, then casting it with the mana produced by the Diamond
Some common types of interaction include removal spells, counterspells, and cards that make it difficult for opponents to attack you
Blink decks, also known as flicker decks, aim to use effects that exile their own permanents, then returning them to the battlefield in order to repeatedly reap the benefits of powerful enter the battlefield triggers
Forcing him to attack is a necessary way to prevent his ability from getting too out of control, but even then, there are plenty of ways of giving him some evasion
This is down to the three all-new, mechanically-unique legendary creatures it brings to the table