Here is a wordy but interesting mechanic I made for a B/R Dwarf faction. The Ghurzad are greedy and reckless in their neverending search for gold.
Dig [Number](Exile the top [Number] cards of your library, then put a colorless Gold artifact token onto the battlefield for each land card exiled this way. They have “Sacrifice this artifact: Add one mana of any color to your mana pool.”)
It’s red because it’s reckless, and it’s black because it’s greedy. Giving up cards in exchange for ramp/artifacts is clearly B/R to me.
I just looked back at my Burning Blade Elite card from a few weeks ago and I figured that this mechanic needed some reworking. I finally came up with a version that I like and that I might use in a future custom set/duel deck: Reflection. What’s cool about it is that it can be used both defensively and offensively.
Reflection [Cost](Whenever this creature becomes the target of a spell or ability, you may pay [Cost]. If you do, put a token onto the battlefield that’s a copy of this creature and change the target of the spell to that token.)
Note that this ability can be chained and used multiple times if you have enough mana to affort it.
One of my favourite Dungeon & Dragons race deserved to be transformed into MtG cards. I really focused on their name to create the gameplay I wanted them to fit in. Without any surprise, they are obviously Blue and Black. They share a racial mechanic which I named Mindflay.
Created for the Winner Is The Judge #411: Evergreen Showcase Cycle on Reddit. The contest was to design a vertical cycle (common, uncommon, rare/mythic) that showcases one (or more) of the new evergreen abilities Menace, Scry and Prowess.I decided to use all three in a crescendo that represents the ascension of a Necroz Order initiate (monks that worship Death). To do so, I had to bring Prowess to black. In my opinion, casting noncreature spells is even closer to black than it is to white, so I don’t really break the pie here. It works both flavorfully and mechanically.