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Converting Rules Cyclopedia Monsters to 5E

by Sheldon Morris

Alright. This is the beginning of a trip through the RC in an effort to convert any monsters to 5E that do not appear in the Monster Manual. I debated with myself about placing this in the Mystara forum since it concerns Mystara-specific content, but in the end I believe this is more about the 5th Edition system than a setting.

What I intend to do is probably post a creature's stat block, followed by notes and comments on how and why I ended up with what I did. From there, I hope to have some discussion on other options and considerations that could improve the creature, be it from a balance or play standpoint.

So, I hope that this sparks some interesting conversations about how to handle Basic D&D monsters in the 5E paradigm. I believe that exploring the behavior and nature of some of these monsters, and how that translates into game mechanics (both in Basic and 5E), is quite interesting.

And, at least this thread may provide people with additional creatures for their 5E games!

The first creature up is in fact the first creature listed in the RC's Monsters section - the Actaeon! I'll start him up in my next post.

[Edited to add my checklist.] This lists the Creature name, what its CR is in basic D&D's Rules Cyclopedia (RC) (according to my formulas), the D&D 5E CR that it has been converted to, and if the conversion has been "done" or I have yet "to do". To shorten the length of the post, the table has three columns across. I hope this is alright to do.
I have now added links where any creature is listed as "done" to bring you directly to the post. Thanks to enderxenocide0 and Tim Baker for the suggestion and how-to!

[Edited for update.] As you can see, the table tags are no longer functioning on the forum (although I have been told people are looking into it, which I am very thankful for). I have removed the table tags so that the links are working again, even though it's still a mess. Remember that there were 3 columns, so there are still 3 creatures listed on most of the lines. And YES, I will (have) return(ed) to this project!
Added - I've tidied this all up so that it's all one column now.. one LONG column though. But at least it's far more usable now.

Creature CR (RC) CR (5E) Checklist
Actaeon (Elk Centaur) 6 6 done
Adaptor 4 4 done
Aerial Servant (Haoou) 8 8 done
Ant, Giant 2 1 done
Ape, Snow 1 1 done
Ape, White 1 1 done
Archon 17 - to do?
Athach 6 10 done
Baboon, Rock 1/2 1/2 done
Rock Baboon, Alpha Rock - 1 done
Bear, Cave 3 3 done
Beetle, Giant Oil 1/2 1/4 done
Beetle, Giant Tiger 1 1/2 done
Blackball (Deadly Sphere) 12 - to do?
Caecilia 3 3 done
Cat, Mountain Lion 1 1/4 done
Crocodile, Large 2 2 done
Devilfish - - to do
Djinni (Greater; Pasha) 9 - to do?
Dolphin 1 1 done
Dragon Ruler, Pearl 23 - to do?
Dragon Ruler, Opal 27 - to do?
Dragon Ruler, Diamond 30 - to do?
Dragon Ruler, The Great One 45 - to do?
Drake, Mandrake 1 1 done
Drake, Wooddrake 2 2 done
Drake, Colddrake 3 3 done
Drake, Elemental 4 4 done
Drolem 15 15 done
Efreeti (Greater; Amir) 12 - to do?
Elephant, Prehistoric 4 4 done
Faerie (+ Leader & Elder) 1/2 1/2 done
Ferret, Giant 1/4 1/8 done
Fish, Giant Bass 1/2 1/4 done
Fish, Giant Rockfish 2 2 done
Fish, Giant Sturgeon 5 5 done
Gargantua, Carrion Crawler 11 11 done
Gargantua, Gargoyle 14 - to do
Gargantua, Troll 25 - to do
Giant, Mountain - 11 done
Giant, Sea - 10 done
Golem, Wood 1 1 done
Golem, Bone 3 3 done
Golem, Obsidian 3 3 done
Golem, Mud 4 4 done
Golem, Amber 5 5 done
Golem, Bronze 10 10 done
Grab Grass 1/4 - trap?
Green Slime 1/2 - trap?
Gremlin 1/2 1/2 done
Haunt, Poltergeist 9 2 in MM
Helion 4 4 done
Horde 1-9 2,4,7 done
Hsiao (Guardian Owl) 2-10 2,4,9 done
Hydrax 3-7 5 done
Kryst 4 4 done
Lava Ooze 3 3 done
Leech, Giant 2 2 done
Lizard, Giant Gecko 1 1/2 done
Lizard, Giant Draco 2 1 done
Lizard, Giant Horned Chameleon 2 2 done
Lizard, Giant Tuatara 2 2 done
Locust, Giant 1/2 1/8 done
Lycanthrope, Werebat 1 2 done
Lycanthrope, Werefox 1 2 done
Lycanthrope, Wereshark 2 3 done
Lycanthrope, Wereseal 2 4 done
Lycanthrope, Devil Swine 4 6 done
Malfera 6 6 done
Manscorpion (Warrior & Cleric) 5,11 5,11 done
Manta Ray 2 1 done
Manta Ray, Giant 5 5 done
Mek 6-8 8 done
Metamorph 2 - to do
Mujina 4 4 done
Neanderthal (Caveman) 1/2 1/4 done
Nekrozon 4 4 done
Nightshade, Nightcrawler 20-24 22 done
Nightshade, Nightwalker 16-21 19 done
Nightshade, Nightwing 12-16 15 done
Nixie 1/4 1/4 done
Nuckalavee 8 7 done
Phantom, Apparition 7 7 done
Phantom, Shade 8 8 done
Phantom, Vision 8 8 done
Phoenix, Lesser 9 8 done
Phoenix, Greater 13 13 done
Plasm, Lesser 3 3 done
Plasm, Greater 5 6 done
Pterosaur, Small (Pterodactyl) 1/4 0 done
Pterosaur, Large (Pterosaur) 4 1 done
Revener 5 5 done
Rhagodessa 2 2 done
Robber Fly 1/2 1/4 done
Roc, Small 2 2 done
Roc, Large 4 5 done
Salamander, Flame 4 4 done
Salamander, Frost 5 5 done
Shadow 1 1 done
Shark, Bull 1/2 1/2 done
Shark, Mako 1 1 done
Shark, Great White 3 3 done
Shrew, Giant 1/4 1/4 done
Slug, Giant 5-10 5,9 done
Snake, Spitting Cobra 1/4 - to do
Snake, Giant Racer 1/2 - to do
Snake, Pit Viper 1/2 - to do
Snake, Sea Snake 1 - to do
Snake, Giant Rattler 2 - to do
Snake, Rock Python 2 - to do
Spectral Hound 3 - to do
Spider, Giant Crab 1/2 - to do
Spider, Giant Black Widow 1 - to do
Spider, Giant Tarantella 2 - to do
Spirit, Druj 10 - to do
Spirit, Odic 11 - to do
Spirit, Revenant 12 - to do
Sporacle 4 - to do
Statue, Living Crystal 1 - to do
Statue, Living Iron 2 - to do
Statue, Living Rock 2 - to do
Termite, Swamp 1/4 - to do
Termite, Fresh Water 1/2 - to do
Termite, Salt Water 1 - to do
Thoul 1 - to do
Toad, Giant 1/2 - to do
Toad, Rock/Cave 1 - to do
Undine 6 - to do
Whale, Great 16 - to do
Whale, Narwhal 4 - to do
Yellow Mold 1/2 - to do