Gonna go with 3 cards that haven't been mentioned:
I love BW Humans as an archetype, and the Lieutenant gives you another copy of Champion of the Parish that can also be played as an anthem for your team if you've gone wide enough. It's an excellent card to push yourself vertically after going horizontal, can generate the same lines of play as the Champ, and it's just a clean design. Probably the best tool that aggressive W/x archetypes have gotten in a long time.
This card has such a weird body but it plays very uniquely. I've found in my time playing the game that players hate trading down and will often end up racking way more damage than they should because they refused to lose out on "value" by giving up creatures for something lesser. Kari's body makes her kind of awkward to block and commit resources towards, often times players will just let themselves get nugged for 1 because hey, it's only one point of damage right? That line of reasoning does fall apart when they let the monkey continuously get in for two as well though. If they have something to just eat the monkey each combat, alright no problem. But if they actually are forced into thinking about trades? I've seen a lot of players just take the full 3 damage across two bodies because they deemed no good blocks. She's evasive, leads to interesting attacks, wears buffs and equipments like a champ, and plays even better with any way to maximize the multiple bodies (Purphoros triggers, anthems, etc.). Just a fantastic card.
Other people might find it to be a bit too much value generated, but I just love the steady card advantage that it helps to generate to grind away in the late game. 3/2 is a fine base body, and when you start creating multiple clues you open up so many new lines of play. The biggest issue with ramp decks is running out of gas or having your big ramped threats answered easily and then being left with nothing. With a Tracker out, you have the chance to stockpile some clues to crack in the later game and recoup resources. It's just another clean design that I really love and it has quickly become one of my favorite cards to play with.
Bonus because this card is too much fun:
Big old body with Deathtouch, Exploration effect, and a way to draw cards and churn through your deck in the later game. Finding ways to trigger multiple draws is the best, nutty with fetches and anything that self-mills and puts lands in the bin. I've found this to be an incredibly fun and interesting creature for drafters to play around with, and it creates an interesting little game of eating away at your own resources unless you can somehow maximize its presence on the battlefield and take advantage.
