I have for a long time wanted to skin MTG with the names and images from /r/bossfights

In some of the tries below I didn't realise the URL is unique to a card. In others, I did, but I copied the URL too soon and it points to an earlier card.

First, some random generation, without "Advanced Options"

  Curse of Cripling Memory 
  [Image: Maybe a laboratory? Someone with his face fading in a dark cloud?]
  1U
  Instant
  Choose a Creature type. You may cast creature spells as though they had flash.
  (The blades of the unskilled never rust)


  Cloud Portal
  3
  [Image: clouds, something that could be a flat-top pagoda, maybe runes on the
  clouds?]
  Artifact
  3, {T}: Draw a card.
  (Even a whisper can still be heard above the rest of the world.

https://www.urzas.ai/cards/?card_id=78e7e720-c965-45f8-82ca-...

  Dusk Hovergard
  2U
  [Image:A blob with a blob next to it]
  Creature - Spirit
  Flying
  When Dusk Hovergard enters the battlefield target creature can't block this turn
  1/1
  (Can't read the flavour text because the card text is white on white background)

  Morbid Regimen
  2{B}
  Enchantment - Aura
  Enchant creature
  Enchanted creature gets +2/+2
  (Once each night, the sleeper awoke to find his house had been transformed into
  a death garden.)

The following were made with "Advanced options": name, mana cost and type chosen by me.

  Booby Trap
  2B
  [Image: something steampunk?]
  Enchantment
  Whenever a creature attacks, sacrifice Booby Trap unless you discard a card.
  (When the lives of Naya used to be short, he never lost his temper. Now he just
  smiles)

^ I was trying to get it to geneate something offensive, I confess.

  Black Thunder
  BBB
  [Image: a threatening cloacked figure with pink thunder around its head]
  Sorcery
  Each player loses 1 life.
  (Forged from the same material as the hilts of a star shell, the power of the
  Raegstrom can't be blocked by armor.)

  Helm of Fire
  1R
  [Image: Kind of a melted helm, ok]
  Artifact - Equipment - Equipment
  Equipped creature gets +1/+0 and has haste.
  Equip 1 (1: Attach to target creature you control. Equip only as a sorcery)

  Sea of Knowledge
  4U
  [Image: A nondescript landscape, perhaps with thralls?]
  Instant
  Put target card from a graveyard onto the battlefield under your control
  ("Let the spirits of the dead join the living" - Nicol Bolas)

  Word of Might
  [Image: A nondescript figure perhaps with wings, in front of a colorful
  landscape]
  4G
  Enchantment - Aura
  Enchant creature
  Enchanted creature gets +2/+2
  ("The law is one stone cannot be broken" - Xantcha, ancient astronomer)

^ I only asked for "Enchantment" on this one but it correctly added "Aura" to match its Ability.

  Guardian of the Peace
  [Image: A nondescript figure, perhaps in desert attire, in front of what could
  be an abstract rendering of a modern city's skyline.]
  WW
  Creature - Human Soldier
  {W}, {T}: Destroy target attacking or blocking creature.
  (When the silver finds her feet, it grants her sisterhood. Only one person will
  survive).
  2/2

^ In this card too the Tap symbol has a red hue. Why?

  Scorching Sunset
  5RR
  [Image: abstract tiles that could be fields with what could be a burning palace
  in the background]
  Sorcery
  Scorching Sunset deals 3 damage to any target.
  (Once the flames begin to subside, the spark is forgotten)

  Mana Bomb
  5
  [Image: Maybe a kind of mock-oriental cauldron or boiler? Nondescript background
  that could be attempts at reproducing ideograms?]
  Artifact
  {T}: Add {R}, {W}, or {U}
  (Amass in corpse and feed it)

Let's try a few curveballs.

  Lightning Bolt
  {R}
  [Image: a nondescript view of what might be clouds with a yellow shape that
  could be a bolt]
  Instant
  Lightning Bolt deals 3 damage to any target.
  (If you can see the clouds, the lightning will strike.)

^ OK, so if we give it the name, cost and type of a known card...

  Llanowar Elves
  {G}
  Creature - Elf Druid - Elf Druid
  {T}: Add {G}
  (As the evil spirit called the spirits of the dead, so the holy fire of
  Llanowar, and our lifeblood, we bow in honor to them and the fire that would
  never die)

  Dark Ritual
  {B}{B}{B}
  [Image: nondescript hooded figures perhaps conducting a ritual]
  Sorcery
  Each player sacrifices a creature. You gain life equal to the life lost this
  way.

^ Ah-hah! Dark Ritual has not seen nearly as many reprints as Bolt and Elves, so it can't be reproduced as easily. My theory.

  Honda Array
  {P}{}{} (Empty mana circles)
  [Image: could be a distorted rendition of a car?]
  Factory - Car Factory - Vehicle 
  Horsepower (P/P) (P/P) (P/P) (P/P) (P/P) (P/P) ....  (P/P) (

^ It can sort of generate nonsense but not quite. Also, it can't close parens. Typical.

  Colossus of Rhodes
  11
  [Image: clearly a distorted image of a giant status in front of an abstract city
  with sea]
  Statue
  When Colossus of Rhodes enters the battlefield, exile target artifact or
  creature.
  (Those who could tell of a scepter, one end of the alphabet, and dawn.)

^ What? What could those people do? Anyway it will happily generate cards with nonexistent (base) types.

  Donald Trump
  {}{}{} (Empty mana circles)
  [Image: could be Donald Trump and Imperial Palace Guards]
  POTUS - Don'task target creature.
  1{U},{T}: Draw a card

  areoiarg;iargea
  a;eroigja;oerijg
  [Image: a surrealistic depiction of people in kind of georgian dress?]
  a;rgoijaer;oigjaerg - a;rgoijaer;oigjaerg 
  ifnd has access to look at the top card of target player's library.
  (it's almost a month after they've shuffled)

^ They can't be playing a combo deck then.

  Mark Rosewater
  {} (Empty mana circle)
  [Image: no idea. Something out of Bladerunner?]
  Boss
  2, {T}: Create a 0/1 colorless Clue artifact creature token.

OK, I'm out of ideas.

Conclusions: a) The ability text is not bad. Sometimes it makes sense, sometimes it doesn't.

b) It has absolutely no clue of the relation between mana costs and abilities, but that's fine because neither does WoTC.

c) It will happily reproduce existing cards, but probably only if they have many reprints.

d) Forget about generating coherent images.

e) Forget about generating coherent reminder text.

For the last two tasks in particular, images and character text, my hunch is that one would need to train on way, way more M:tG specific data. Or it might need a separate system trained on a different prompt, because it doesn't seem to find enough information in the generated card text or fluff.

Verdict: MaRo's job is still secure.

Also, having seen the attempt at M:tG Salvation that I think powers RoboRosewater, this is not a substantial improvement over that. It would be if it could produce meaningful art, but. No.

To add to that point, decks can be good or bad based on the ecosystem (meta) they're playing in. A deck that aims to rush you down might be great in a meta where players expect slow decks, but terrible in a meta where many decks have means of healing themselves.