These various UB sets have me craving more niche IPs. So this is a recent ongoing favorite done as a signature spellbound style.
Jason Asano 2WB
Legendary Creature - Avatar
At the beginning of each end step proliferate. T: Jason Asano deals 1 damage to target attacking or blocking creature.
Tyranny of Rank 2WR
If a source would deal damage to a permanent with Mana Value greater than its own, it deals half that damage rounded down instead.
If a source would deal damage to a permanent with mana value less than its own, it deals double that damage instead.
Feast of Absolution 3BB
Remove all counters from all permanents. You gain one life for each counter removed this way. Add B for each counter removed this way.
Harbingers of Doom 2B
Enchantment - Aura
Enchant creature with a counter
At the beginning of each upkeep choose upto one target creature. For each counter on enchanted creature, put the same number and type of counters on the targeted creature. Then create a copy of Harbingers of Doom and attach it to that creature.
Colin, Sanguine Horror XXB
Legendary Creature - leech
Colin enters the battlefield with X +1/+1 counters.
Remove a +1/+1 counter from Colin: Regenerate
Whenever another creature dies, exile it and put a +1/+1 counter on Colin.
If there are ten or more +1/+1 counters on Colin it has hexproof and indestructible.
[If a player lost life this turn, Jason Asano can't be countered.]
Maybe even, [if a player lost or gained life] since it's white black.
I kinda feel like the proliferate should have more interactivity going on, limitation possibly for it. Proliferate is such an abused function, along the lines of indestructible and menace. I hold high standards for keeping it interesting where it's implemented.
Tyranny of rank is kinda interesting, but the cost is dreary. Maybe it's just personal preference, but I like enchantments to be light and technical. In the three range maybe at most. When I'm etching out a competitive concept, this is what I look for. This would get passed over in favor of something like Goblin Oriflamme or Bad Moon despite its potential.
I think feast is way too slow, and it would likely cost the same as Damnation if it saw print.
Harbingers would be simpler to just amend [double the number of counters on target creature] as a functionality. Having to describe counter types or cover them individually when you're interacting with them is dreary and I really loathe it.
For Colin, [If a creature would die, exile it instead.] is necessary since it changes from permanent to card through zones. Also, it will cover the functionality since rules define "dies" covering that cross between zones.
jason should probably be on your end step, and even then it probably should have some sort of condition to activate, like Brimaz, Blight of Oreskos but otherwise its fine.
tyranny of rank seems kind of bad because if all your creatures are a higher cmc than your opponent's your probably winning combat anyway, not to mention its pretty expensive for an enchantment thats symetrical and a little inconsistant.
feast of absolution seems fine even if it is a little bit of a narrow hate piece. it could probably cost 4. its the kind of card i feel like i would see people complain about in commander even though its not that great. but its pretty decent in the niche it fills.
harbingers of doom is a little screwed up because its doubly expotential if you stack the aura multiple times on the same creature. i would just remove the part where it copies itself and maybe make it a creature that does the upkeep effect. but these are cards inspired by an existing property so maybe theres some lore reason it is the way it is.
colin (who is probably supposed to have base power and toughness 0) honestly just seems fine. Maybe he should go up like 1 mana