Fireball:
Lets get the ball rolling with our first cut, Fireball. In most circumstances Rolling Thunder is better at removing multiple targets that it is worth paying an extra Red pip to direct damage to the face.

Hooting Mandrills & Sultai Scavenger:
This was a hard choice to make. Being the green counterpart to Gurmag Angler, getting a 4/4 for G was great. In an environment where it's no longer the biggest thing around and therefore can't be swinging with this card as often anymore, Hooting Mandrills just seems plain boring. Similarily, Sultai Scavenger was competing with bigger bodies that if we delve a little deeper, it just didn't do enough.

Putrid Goblin & Suture Priest:
With First Day of Class gone, and the introduction of cheaper and better sacrifice fodder, Putrid Goblin is looking like a stinker of a card. With the infinite loop of sacrificing Putrid Goblin gone, we can remove the band-aid fix that was Suture Priest.

Skewer the Critics & Dragon Fodder:
This was just Chain Lightning with extra hoops. While this card is amazing, red needed to make space to explore areas outside of dealing direct damage to face and having lots of small creatures. Hopefully this will silence the critics that red is a one-dimensional colour. Similarily Dragon Fodder was much like Forbidden Friendship and Goblin Instigator and needed to make way for newer cards.

Minimus Containment & Otherworldly Journey:
Much like its name, these two cards are being cut for the sake of reducing the cube size to its ideal size. With Bound in Gold, Journey to Nowhere, Minimus Containment seemed excessive. The same can be said with Ephemerate and Ghostly Flicker performing the same thing as Otherworldly Journey but better.

Murder & Doom Blade:
The end of Magic is here! Murder and Doomblade have finally been cut for more powerful cards. With more and more flexible removal spells like Feed the Swarm and strictly more powerful versions like Cast Down it only makes sense that these two would see the end of their days.

Raffine's Guidance:
Sentinel's Eyes provides vigilance and is cheaper to recast. I can see the argument that 2W is easier to cast than eating up cards in your own graveyard.

Raffine's Informant:
Spirited Companion nets you a card, while Raffine's Informant only trades a card. I can see this being an interesting addition for enabling madness or graveyard matters decks.

Security Bypass:
Much like Cartouche of Knowledge and cards with Fly effects, this provides evasion for aggressive blue strategies. It even helps grow the attacking creature, which would be one of the weakest qualities of ninjas.

Midnight Assassin:
Vampire Nighthawk at home.

Mayhem Patrol:
I'm unsure if this is worthy of a spot as it just seems like a mediocre Magma Jet. It doesn't quite live up to the name.

Celestial Regulator:
A decent creature, however requiring counters being present to ensure a frost effect just seems to plain.

Quick-Draw Dagger:
This is a fine combat trick. One of the better flash equipment cards that auto equips on to a creature as it can also be moved around for 1 mana.