Prophet of Kruphix
A bomb is a bomb.
How is it even close to a bomb?
It costs no mana, it makes attacking hard for your opponent if you are holding a card, it makes blocking hard for your opponent if you have a card in your hand and enough mana to potentially bestow something, it allows to pay lategame mostruous costs the same turn you play the creature,you can develop your board and grip tide something...
By definition, that's not a bomb, that's a card that needs other cards to win. Bombs don't need other cards to win--the exception might be Pack Rat, but you draw cards every turn anyway. I think on a 5 scale I put prophet, in Theros, between a 2.5 and a 3, whereas I put the Emissaries and Naiad at 3+s.
Prophet works in theory, but its cost and body is prohibitive. By the time you get to 5 mana, your board and your opponent's board are already developed. Creatures as combat tricks is cool and all, but you're probably not going to have a lot of cards in-hand at that point that matter for the board state. It's also a 2/3. That's a horrible body for 5 mana. Without a way to ensure you have 5-drops or multiple 2- and 3-drops in hand (like drawing cards), Prophet becomes a costly attempt at building a magic Christmasland scenario. I've never seen anyone win with it that wasn't going to win anyway. Additionally, it's a 2-colored-mana card in a fairly weak pack on pick 1. If we pick it now and GU is closed, we just completed wasted a pick.