Training to be a spellcaster on the continent of Auros is a long, arduous process, one that can take several years. As such, many wizards are quite capable of working some magic before becoming a first level wizard, or even before reaching 1st level. And of course, some individuals learn some of the basics of magic, and then abandon their studies, but retain their spellcasting abilities through use, maybe even making a career of their performance. Many apprentice clerics work as physicians in hospitals, and wizard apprentices often work as cleaners or repairmen, although some memorize offensive cantrips and serve as unassuming bodyguards. Sorcerer apprentices often make their way as entertainers.
A 0-Level spellcaster has access to the cantrip spells up to or equal to those that would be available to them at 1st level. In addition, a 0-level spellcaster who utilizes a spellbook may record any cantrip in their spellbook and prepare it as if it was a first level spell being cast by a first level spellcaster. A 0-level spellcaster may change 1 at will cantrip once every d3 moons.
This is mostly useful for creating NPCs, but PCs may choose to become apprentices of a new class following suitable in-game roleplaying, and at a cost of 500 XP. If a PC wishes to make their character an apprentice in a second class at character creations, reaching 2nd level takes 1600XP, at which point 500XP is removed. All following levels require the normal amount of XP.
Apprentice Spellcasters have the HP of the average (rounded up) of their classes Hit Die, plus their Constitution Modifier. For example, a wizard apprentice in 5th Edition with CON 12 would have HP 4+1=5.
PCs who expend 500 XP to gain apprenticeship receive additional HP equal to either ONLY the apprencticeship’s Hit Die Average or ONLY their CON modifier, whichever is higher. For Example, if someone gains a level of Cleric, they will gain HP6 unless their CON Mod is greater than +6. A wizard apprentice with CON 20 would add +5HP, not 4HP. A PC who takes an apprenticeship at character creation takes whichever HP value is lower. A wizard apprentice with CON 20 would take only +4HP.