Mythic rares are designed to feel special, whether that means a story-important character, a game-changing threat, or a card so powerful that it may just end the game outright if left unanswered
All praise Yidris Yidris, Maelstrom Wielder, is a four-mana blue, black, red, and green 5/4 with trample that reads, Whenever Yidris, Maelstrom Wielder deals combat damage to a player, as you cast spells from your hand this turn, they gain cascade. If the spell already has cascade it gains another instance of it, which is very silly
Maximum quantity allowed per order: 6
By contrast, topdecking a Wily Goblin on turn 7 after you just cast your last Glorybringer is pretty much a whiff which is good
Now let's say that I'm the one who opens the Sarkhan instead of you
However, the archetype also includes some Fusion Monsters that are instead Summoned by a regular Fusion Summon, in addition to Main Deck monsters