I have been reading through the Planeshift articles, especially the Bestiaries to get an idea of what to expect from Ravnica's Beastiary.
The way they are organized is heavily by type. So there would be an sections on broad Angel, beasts, demons, horrors, undead, giants, and more particular creatures.
With in each section are a over view of how these creatures fit into the setting, what they look like, and so on. They then either say use the stats from creature X from the MM (or Volo's Guide to Monsters in at least one case), sometimes with a fluff or minor revision to the stat block, and in other cases when a creature is radically different from anything in the MM (or VGTM), they give you a new stat block.
As I understand it his formula will contiinue for GGR. Still I believe they will be more picky about stats from the MM being a good representation of a creatures abilities before they say use creature X's stats to represent Y.
Example Angels for the Planeshift articles just use regular Angel stats, Devas for rank and file Angels and Plantars and Solars for special more powerful Angels. This won't work for Ravnica, because Angels on Ravnica are more diverse in outlook, function, appearance, and powers, as well that Ravnica Angels show no ability to shape shift like Devas do and Plantars and Solars are too tall for Ravnica Angels. They might use Deva, Plantar, Solar stats for Guildless Angels like Angel of Serenity, whose function and place and abilities appear to be less defined on Ravnica is possible.
Demons I think will be a mix, some will just use the stats of regular D&D demons where it makes sense, but obviously Rakdos gets his own stat block, and any demon that stands out as too different from MM demons will get it's own stat block.
For Dragons Niv Mizzet will be in. Pit Dragons and Hypersonic Dragons seem different enough from anything in the MM, so they should get their own stat.
Sphinxes, aside from Isperia who will get her own stat block, will just use the MM stats, about they might remove the time traveling abilities. If they draw monsters from the current set they might have A Nightmare Dream Eating Sphinx stat block.
Drakes I think they will have Crackling Drake at least and maybe Tower Drake as stat blocks.
Most Weirds will be stat blocks, as their is nothing that can properly emulate them.
Elementals will be likely use plant creatures and regular elementals in some cases, but some will require new stat blocks.
Eelhawks might just use hawk stats, maybe with lightening damage, Squidflies might need new stats, and same with Waspcrabs.
Omniphibian will need new stats, no frog creatures in 5e can make it's environment resemble it. Some less frog creature will like just use giant and regular from stats.
One type of Imp will just use regular imp stats, but odder ones like Stink Weed Imp might get their own stat.
I don't think any Devils will get their own stats, I think they will just use regular stats, but with a change in alignment perhaps.
I think Shrieking Gargoyles will use regular Gargolye Stats, but Dominator Gargoyles will use new stats.
Fairies will just use the stats of Nixies and Pixies and the like.
I because Ravnica's Dryads are plant like as MM and Ixalan Dryads, mostly looking like human attractive females with leaves for hair, they will use new stats for them. I could be wrong.
I think the MM Dryads stats will be used for Carven Cryprids instead.
Purple Wurms will be used for one of even several types of Wurm, but not all. Undead and some of the other more Unique Wurms will get their own stats.
I think the Giant Insects of the Golgori will be a mix, some new stats for the more unique bugs.
Giants will likely just use Stone Giant stats, but maybe will an additional abilities depending on the giant's role. Rakdos Giants might use Hill Giant or Frost Giant stats instead.
Archons will get their own stats, there is nothing like them in the MM.
Felidars are Celestials in the Planeshift articles with abilities similar to Unicorns, but more cat like. I think Felidars will still be Celestial and get a stat block, but be made more unique from from Unicorns in abilities.
Specters are too different from regular D&D Specters, they are the black mana version of Archons, but Undead. They might make them unique stats or just use regular specters, but add mounts. Hard to say.
I think some of the Undead will get unique stats, especially the really weird stuff like Necrophilages, others will be get basic undead stats, but in the case of the Orzhov incorporeal undead, will get some kind of special ability or mechanic.
Guildless Vampires will probably just use regular Vampire stats. Orzhov Vampires might use a regular Vampire Stats, or a mix of Regular Vampire Stats and Stats for a Vampire that casts divine magic. Dimir Psychic Vampires and Moroii and Skeletonal Vampire will get new stats.
Thrulls I think will get new stat blocks, they are too different from anything in D&D. Small change they might use Flesh Golems for one type, but I don't think they will be constructs.
There are a variety of unique beasts like Indiks, Alms Beasts, and so on. I think only the ones with unique attacks will get new stats. Alms Beast might just use dinosaur stats. Indiks will get stats I think. Most Gruul Beasts will get unique stats.
Griffons will just use Griffon stay from the MM.
I think a lot of creatures like Minotaur Reckoner will get NPC templates. Unique NPCs like Rakdos will be in the NPC section and obviously get stats.
Most Horrors will get unique stats.
I hope spy bugs get their own stats.
Ultimately I think we will get 30 to 40 new monster stat blocks not including NPCs (of which we get over 10). Plenty of refluffed MM Monsters.
Am I also curious which monsters might find themselves reprinted in future products. My guess, Felidar, Angels, and maybe the Archon, D&D doesn't have nearly as many Celestial creatures as it does fiends, undead, Dragons, fey, and so on, even if you include every celestial Eladarin, Guardinal, and Traditional Arch on type. A demon type or two. Some of the cooler horrors. I don't think Thrulls will, but I hope I'm wrong, I could see Thay creating Thrulls.
Also I hope that the way they do up the fluff for started creatures explores a broader place within D&D then just Ravnica.
The way they are organized is heavily by type. So there would be an sections on broad Angel, beasts, demons, horrors, undead, giants, and more particular creatures.
With in each section are a over view of how these creatures fit into the setting, what they look like, and so on. They then either say use the stats from creature X from the MM (or Volo's Guide to Monsters in at least one case), sometimes with a fluff or minor revision to the stat block, and in other cases when a creature is radically different from anything in the MM (or VGTM), they give you a new stat block.
As I understand it his formula will contiinue for GGR. Still I believe they will be more picky about stats from the MM being a good representation of a creatures abilities before they say use creature X's stats to represent Y.
Example Angels for the Planeshift articles just use regular Angel stats, Devas for rank and file Angels and Plantars and Solars for special more powerful Angels. This won't work for Ravnica, because Angels on Ravnica are more diverse in outlook, function, appearance, and powers, as well that Ravnica Angels show no ability to shape shift like Devas do and Plantars and Solars are too tall for Ravnica Angels. They might use Deva, Plantar, Solar stats for Guildless Angels like Angel of Serenity, whose function and place and abilities appear to be less defined on Ravnica is possible.
Demons I think will be a mix, some will just use the stats of regular D&D demons where it makes sense, but obviously Rakdos gets his own stat block, and any demon that stands out as too different from MM demons will get it's own stat block.
For Dragons Niv Mizzet will be in. Pit Dragons and Hypersonic Dragons seem different enough from anything in the MM, so they should get their own stat.
Sphinxes, aside from Isperia who will get her own stat block, will just use the MM stats, about they might remove the time traveling abilities. If they draw monsters from the current set they might have A Nightmare Dream Eating Sphinx stat block.
Drakes I think they will have Crackling Drake at least and maybe Tower Drake as stat blocks.
Most Weirds will be stat blocks, as their is nothing that can properly emulate them.
Elementals will be likely use plant creatures and regular elementals in some cases, but some will require new stat blocks.
Eelhawks might just use hawk stats, maybe with lightening damage, Squidflies might need new stats, and same with Waspcrabs.
Omniphibian will need new stats, no frog creatures in 5e can make it's environment resemble it. Some less frog creature will like just use giant and regular from stats.
One type of Imp will just use regular imp stats, but odder ones like Stink Weed Imp might get their own stat.
I don't think any Devils will get their own stats, I think they will just use regular stats, but with a change in alignment perhaps.
I think Shrieking Gargoyles will use regular Gargolye Stats, but Dominator Gargoyles will use new stats.
Fairies will just use the stats of Nixies and Pixies and the like.
I because Ravnica's Dryads are plant like as MM and Ixalan Dryads, mostly looking like human attractive females with leaves for hair, they will use new stats for them. I could be wrong.
I think the MM Dryads stats will be used for Carven Cryprids instead.
Purple Wurms will be used for one of even several types of Wurm, but not all. Undead and some of the other more Unique Wurms will get their own stats.
I think the Giant Insects of the Golgori will be a mix, some new stats for the more unique bugs.
Giants will likely just use Stone Giant stats, but maybe will an additional abilities depending on the giant's role. Rakdos Giants might use Hill Giant or Frost Giant stats instead.
Archons will get their own stats, there is nothing like them in the MM.
Felidars are Celestials in the Planeshift articles with abilities similar to Unicorns, but more cat like. I think Felidars will still be Celestial and get a stat block, but be made more unique from from Unicorns in abilities.
Specters are too different from regular D&D Specters, they are the black mana version of Archons, but Undead. They might make them unique stats or just use regular specters, but add mounts. Hard to say.
I think some of the Undead will get unique stats, especially the really weird stuff like Necrophilages, others will be get basic undead stats, but in the case of the Orzhov incorporeal undead, will get some kind of special ability or mechanic.
Guildless Vampires will probably just use regular Vampire stats. Orzhov Vampires might use a regular Vampire Stats, or a mix of Regular Vampire Stats and Stats for a Vampire that casts divine magic. Dimir Psychic Vampires and Moroii and Skeletonal Vampire will get new stats.
Thrulls I think will get new stat blocks, they are too different from anything in D&D. Small change they might use Flesh Golems for one type, but I don't think they will be constructs.
There are a variety of unique beasts like Indiks, Alms Beasts, and so on. I think only the ones with unique attacks will get new stats. Alms Beast might just use dinosaur stats. Indiks will get stats I think. Most Gruul Beasts will get unique stats.
Griffons will just use Griffon stay from the MM.
I think a lot of creatures like Minotaur Reckoner will get NPC templates. Unique NPCs like Rakdos will be in the NPC section and obviously get stats.
Most Horrors will get unique stats.
I hope spy bugs get their own stats.
Ultimately I think we will get 30 to 40 new monster stat blocks not including NPCs (of which we get over 10). Plenty of refluffed MM Monsters.
Am I also curious which monsters might find themselves reprinted in future products. My guess, Felidar, Angels, and maybe the Archon, D&D doesn't have nearly as many Celestial creatures as it does fiends, undead, Dragons, fey, and so on, even if you include every celestial Eladarin, Guardinal, and Traditional Arch on type. A demon type or two. Some of the cooler horrors. I don't think Thrulls will, but I hope I'm wrong, I could see Thay creating Thrulls.
Also I hope that the way they do up the fluff for started creatures explores a broader place within D&D then just Ravnica.
