In Realm of Existence, 1 "XP" (Experience Points) is equivalent to 10 "ESS". (Essence)
In RoE, you start with 3500 ESS at level zero.
Leveling up is not automatic, going from level zero to one is free.
Leveling up costs the amount ESS that would be equivalent to the amount of XP required normally.
You must spend 10 nights rest every newly acquired level before each takes effect with the exception of obtaining level 1.
You may purchase new levels from any Diety/Totem in prayer/meditation while within a place of rest, a spritual memorial, within a santuary of protection, or under the guidance of a priest or other type of spiritual leader.
In RoE, you can be up to 10000ESS (1000XP) in debt.
Save throws cost 100XP to perform.
Ressurection throws cost 350XP to perform.
In RoE when you don't have enough XP in reserve nor XP debt remaining available to do a save/ressurect throw, you instantly die.
Every increment of 10 levels starting at a whole multiple is 15 addtional root slots. The only exception is when less than level 10, which affords no slots at level zero, and 15 root slots from levels 1 through 9.
Instead of encumberance, in RoE, every proficiency, special ability, weapon, item, piece of equipment, spell, minion, or container requires 1 slot.
Containers may contain addtional slots within under the same rules; however they may be government to be a specific type from this list, limited to a specfic or selection of specfic items, and the slot count may be multiplied by the amount of said container in its parent slot. Also, containers may be limited to containing other containers smaller that the parent container.
It is not recommended to distribute as many proficiencies, special abilties and spells as possible, due to needed spare slots for equipment and items, as it is very difficult to unlearn such.
You can have up to either 999 or the max for the entity and/or parent container of the same item, minion or piece of equipment per the same slot.
You can hold up to 1000 of the same type of of platinum/paladium, gold, silver, or copper pieces per slot, unless the container calls for a higher tally.
For every five slots with proficiencies, special abilities, and/or spells with 100% mastery, five new slots are obtained; however, additonal slots gained via level-up and/or for only the root container.
All proficiencies and special skills in RoE consume one slot, however profiencies and special skills cost the essence equivalent of 10 XP per percent of mastery per how many regular slots it would otherwise normally if not for this player's handbook update, have required.
Mastery of a proficiency or special skill below 10%, counts as no effect for proficiency, therefore it isn't worth purchasing less than 10% of mastery for profiencies and special skills.
Class-Specific proficencies are at 50% discount, Sub-class specific proficiencies are at 75% discount, and Sub-class kit proficiencies are at 80% discount.
One can purchase and improve mastery of proficiencies for the normal cost from any merchant that has them, up to the NPC's own level of mastery.
There is a 7 day delay for every 10% of newly acquired proficiency mastery to take effect.
Spells upgrade in the same manner as proficiencies, however they cost three times as much; in RoE, level 10 is full mastery of a spell.
Spell discounts are governed under the same guidelines as special abilities.
One can purchase and improve mastery of spells for the normal cost from any merchant that knows them, up to NPC's own level of mastery.
There is a 7 day delay for every 10% of newly acquired proficiency mastery to take effect.
Identical henchmen may fill the same slot up to its Minion container capacity.