A 6/6 for only two mana, Kroxa is sacrificed as soon as it is played if it wasn't played via the escape mechanic
They arent the same card, but if youre playing one then you ought to consider the other and the Vanquishers is closing in on 200,000 decks total
So Nicol-Bolas who is basically the big bad has sent Tezzeret (who is also a bad guy planeswalker), to Kaladesh to retrieve an artifact from a fair that the plane was having
You wont really be slamming this turn after turn, maybe once or twice if youre lucky, but thats it
1 Once youve played Herald of Eternal Dawn, youre not (realistically) casting anything else that turn, so its less a question of how youre gonna hold up to cast a Counterspell after doing a bunch of stuff and more a question of if you can make at all
If a door is locked, that room does not contribute to the mana value while the card is on the battlefield