Sullivan set the bar for a red direct-damage spell at Shock (one mana, one card, 2 points)
Now an Enigma Drake can get bigger and bigger over the course of a game while Invade the City's base size is going to be fixed once (unless modified by other Amass cards)
I find it best to let this art and the cards speak for themselves, so lets move forward to some details
It's not perfect, as you can miss, but we've found that four is a good number, where you hit a vast majority of the time
It even tracks rules for you, puts counters where necessary, parses seemingly complex game mechanics, and prevents you from making illegal moves
Rev, Tithe Extractor Rev, Tithe Extractor restricts you to black, but does a great job of ensuring you have deathtouchers on the attack