DnD House Rules
Asmythe was not designed for Dungeons and Dragons, but with a few tweaks it works well enough. Review the Almanac before you continue reading. The changes here are based on D&D 5E but are the same for most versions of D&D and Pathfinder.
Races
In Anmythe there are only four major races: Humans, Elves, Dwarves, and the Goblinoids. For the most part, these races can be considered the same as those described in the Players Handbook.
There are no half-elves, half-orcs, or any other half-race in Asmythe. Only the Ilthids had magic strong enough to make that happen and they don't exist anymore.
Goblinoids (Orcs, Goblins, and Hobgoblins) are not playable races.
Other races described in the Players Handbook _could_ exist as "lost" races, created by the Ilthids and forgotten. Playing these races (Halfling, Dragonborn, Gnome, Tiefling, etc.) is strongly discouraged. If a tribe of these exist in the campaign setting, they would probably be viewed as uncivilized savages or beasts by any of the civilizations.
Classes
I find the class system in D&D to be overly restrictive, but for the sake of coherence it remains unchanged. Except as described below.
Personality and Background
Asmythe is a story driven world. Personality and backstory are more important than any statistic on the character sheet.
Alignments are just a vague guide, players should also consider inspirations, motivations, fears, and other personality traits.
There are only four widely spoken languages in Asmythe, read the Almanac for details. If the language isn't listed there then it is either lacks the structure and syntax to be a real language, or it is a supernatural language which would result in insane and death if anybody in Asmythe attempted to learn it.
Equipment
For the sake of simplicity, the equipment lists in the Players Handbook can be considered canon, especially within the Empire. Each of the four races will have their own variation on different types of equipment, Elven equipment will be made of plants for example, but the equipment given serves well enough for most campaigns.
Spellcasting
Magic in Asmythe is very different than magic in D&D. Read the chapter on the Supernatural for a complete description on how magic works in Asmythe.
Spellcaster in Asmythe aren't bound by the spell lists given in the Players Handbook, instead they have access to any spell that fits within the scope of the type of magic they use. But they can only know a limited number of spells. When selecting spells for your character you may select from any of the spell lists, as long as the spell effect fits within the type of magic: Dragon Magic or Arcane Magic. Some spells don't fit either and may not be selected, such as mending and most transmutation type spells.
Dragon Magic casters know 6 spells at character creation and can learn up to a total of 6 *Character Level spells, of any level. Cantrips count against the total number of spells a caster can know. A caster may "forget" a spell to learn a new one. Learning Dragon Magic usually involves a lot of meditation and practice, almost always with the help of a tutor already familiar with the spell.
Arcane magic casters know 6 spells at character creation and can learn any number of spells. But arcane magic is extremely dangerous to keep in your mind. Arcane casters must keep a "spell book" to record the spells they know but the only limit to the number of spells they can have recorded is the number of books they have. An Arcane caster must always have access to their spell book to cast a spell, even cantrips. Arcane magic can be learned from a tutor, which may be an outsider, or copied from a source such as a spell book.
Spellcasters are less limited in the number and "level" of spells they can cast than in standard D&D. Each class has a number of "spell points" equal to the sum of (level * spell slots) for each level of spell. For example, a third level Wizard has 4 first level and 2 second level spell slots, they have 8 spell points (4*1 + 2*2); a 9th level wizard has 36 spell points. Casting a spell uses spell points equal to the level of the spell.
Normal spells have no material components. Rituals always have material components.
Classes
Bard
Bards use Dragon Magic, with music as a focus. They do not usually pledge themselves to a specific cosmos but use whichever dream is convenient. Bards must always play music to cast a spell.
= Cleric/Paladin
Clerics are the ultimate Dragon Magic casters. They pledge themselves to a Cosmos and spend their lives spreading those beliefs throughout the world. Any spell with an effect opposed to their cosmos costs twice as many spell slots to cast.
Paladins as a character archetype are classic and you are encouraged to play one. However the class as described in the Players Handbook do not exist in Asmythe. Instead, play a combat focused cleric with an appropriate personality and background.
All the special abilities of a paladin are available to clerics as feats.
Druid/Ranger
Druids are also Dragon Magic casters with a focus on nature and wild things. As with all Dragon Magic it is important to remember that druids can not create something from nothing. A "summon plant" is actually a "locate plant" spell would not be able to find a cactus in a rainforest, for example.
As paladin is a sub-class of cleric, ranger is a sub-class of druid and doesn't exist in Asmythe as described in the Players Handbook.
All the special abilities of a ranger are available to druids as feats.
Sorcerer
This class does not exist in Asmythe. A creature with innate arcane magic can only come from the outer planes. (Or be an Ilthid, which don't exist anymore.)
Wizard/Warlock
Wizard is the ultimate arcane magic user. Wizards must always cast spells from a spell book, or other written medium, containing the spell they are casting.
As with paladins and rangers, warlocks are only a special kind of wizard. Players may build a personality and backstory appropriate to a warlock-lick character but on paper they exist identical to a wizard.
Warlock special abilities are available to wizards as feats.
Martial Classes
Monks, Barbarians, Fighters, and other non-spellcasting classes with super abilities rely on Dragon Magic for those abilities, although their magic comes from a mastery of self and is far more strictly defined than spell casters.