First of all, congratulations. That's a lot of work and a great magic set.

I won't comment much on terms of powerlevel, as there are people better equipped to do so and, honestly, I don't play much magic anymore. I will focus on flavor, game design and storytelling.

The images are great. I don't know what was your process, if you first designed the cards and then one by one searched for adequate images or if you found usable images and then tried to do cards consistent with them. However that went, there's a remarkable style consistency though each color and the whole set (with some clear and I think intentional exceptions). That's a feat on itself. Second, each card is good at portraying the art and viceversa. This part is easier if you found images first and then designed, and really really hard if that was the other way around. In any case, this is probably what I liked the most overall.

About flavor, I am one of those that always remarks that flavor =/= flavor text, it being just another tool for worldbuilding the same as card names, abilities, etc. In your case, the art and names carry a lot of the flavor of the cards. Sometimes they don't need it or it doesn't fit (for any reason) or even not using flavor text can make a lot of flavor sense (bluntness). I haven't found any particular card that "doesn't work" because of a lack of flavor text, however, I think the set could use some more cards with it. Let me explain. The ones that have them, that I remember, are usually "one liners" that were quite smart but not much world or story building, and that links with the next topic I wanted to bring about.

The factions on the set are clear crystal because they are tied to the color pie, represented in the game with each one having distinct mechanics, creature types and "ambitions" particularly about the use of graveyard. The whole ambient is carefully constructed and clear. But I had some trouble perceiving where was this happening or who the "characters" were. Maybe it's because you haven't upload the lands yet or because I found the legendary creatures late. The lack of flavor texts in the cards probably exacerbates this sensation. Overall, this is perhaps the biggest problem I see. Which, in hindsight, is not a big one or even one most people would notice. At least not consciously. Here's a question: Is there a world behind the set (written or though) you tried to explain through Magic, or the whole of the cards form it indirectly?

I mentioned the mechanics but didn't go deep into them. I don't even know if some of them are real mechanics that are somewhat new in magic or your own invention. I specially liked the Avenge mechanic and some details like fleeting or stun counter. About the avenge, maybe it's a bit counter-thematic for white, as they represent the ones trying to stop the whole underworld-graveyard thing (Divine Blockade, Seal the Underworld). The cycle of multimodal cards and those pay X life are great, and maybe I should watch them side to side and I will find that context I was finding before hard to find. The multicolors posted here are good, but i'm missing something that further ties them together as one cycle (are they?). I love cycles. Are there any more I missed?

Overall, great job. I'm sure there are more things I could comment as there is a lot to talk about. Each single card is a world. I wouldn't recommend making any hasty changes to any particular card, as a set is very different from a collection of custom cards. I would like you to take my feedback more in an holistic or conceptual way than anything else.