Before I get to the judging, I want to ask something. If this contest continues, how many people in this group will participate? It seems like a bit of a pointless endeavor to run a monthly contest and have two or three participants. Please comment below if you're interested in participating, as well as continuing the contest.
Now, on to the reason you all are here: WHO WON!?
has asked to not be considered for the contest, seeing as he helped with the theme for the contest. So, on to our Two contestants.
First, we have KorosukeDoom149's Vengeful Angel
Your keyword is interesting, but the excecution for the ability, as well as the card itself needs a bit of work. First off, the card itself is extremely powerful. I don't know if you've played many drafts/prereleases/other sealed events, but a 3/3 flyer for 3 mana is an auto-include in any deck that can play it. A 3/3 flyer, with an ability, at three mana, at Common is nuts. Most uncommon creatures with that cost and P/T have some sort of downside to offset their power in limited formats. Personally, I would switch it to a 1/4, maybe 2/3 and make it uncommon.
As for the ability, it's pretty hard to keep track of. Maybe, before submitting a four year old card, you could try updating it a bit. That being said, if I was to re-word it, it would look something like this: Grudge 1(Whenever this creature is dealt damage by another creature, put a Grudge counter on that creature. Whenever this creature blocks or becomes blocked, it gets +1/+1 for each Grudge counter on the blocked or blocking creature.) The reason for the counters is that it can be extremely hard to keep track of which creature did damage, and how many times. There needs to be some sort of counter to track that. Also, it would promote synergy with other grudge cards, since the counters do not go away. Otherwise, other creatures would rarely deal damage more than once or twice, making the ability rarely be relevant.
Next up, we have NO8ODY's Vengeful Spirit
Strangely enough, your card has the opposite problem. I'd say that this guy is overcosted by 1, personally. Also, depending on the tribal content of the set this is in, this could be an average of anything from 2/2 to 4/4. As for the ability itself, the flavor may work specifically for that card, but how many other cards would this honestly work for? Would they all have to be spirits? I don't see much flavorful expansion for this.
I can see that you left it open for other things, like artifacts or planeswalkers, but perhaps it's a bit too open. Does it only make creatures bigger, is it like Ferocious where it can create other effects? Maybe it should be restricted to the various colors. Not to mention, this is a mechanic that works better the farther behind you are. The more of X thing that the other player has, the better their board state is, the stronger your creatures get. But if they have enough creatures for Grudge to be effective, they may also have what they need to win the game.
In general, the ability is not very well defined, and unfortunately, without any more explanation or examples, I can't judge this ability very well.
And the winner is:
Both cards were not complete designs. Be it flavor, balance, or wording, there are problems with both cards. That being said, your version of Grudge makes much more sense flavorfully, and is a much more complete design, and the goal of the contest was to design a keyword.
You have the next contest, theme, judging, the whole shebang.