Rules of Travel

The Beast World is surrounded by other realities, running adjacent, parallel, and throughout its physical and cosmological space. Each of these other worlds has its own means of access and physical laws. Some are bustling with life and activity, while others are almost completely empty. 

Magic on Other Worlds 

Different spellcasters face unique challenges when traveling to other worlds. Here are the implications of crossworld travel for each source of magic. Multiclass characters determine their primary source of magic based on whatever class they have the most levels in (or the class they took levels in earliest, in the case of ties). 

Arcana (bard, fighter, rogue, sorcerer, wizard) 

The Arcana of every world is unique and so are the means to cast magic from them. Any Arcanadependent spells cast on other worlds might have unpredictable effects, unless the caster has undergone special training to use magic outside their native world. 
The Broken World lacks any Arcana at all. The power of its Ghost God can be channeled with many of the same techniques, but the effects of casting spells are most unpredictable in the Broken World. 
For Players. Roll a d100 whenever you cast a d100 in a different world. The DM will be in contact with you regarding your magic is affected.

Divine Providence (cleric, paladin) 

While deities only hold direct sway over the world they observe, they can still see other worlds and interact with them. Granting divine servants their spells while in another world requires the deities to speak their power through the Absolute Veil, which can have unpredictable effects on the most potent spells they cast. 
For Players. When a cleric or paladin finishes a long rest and prepares their spells, roll a d100 for each slot of the two highest levels they can cast. The DM will be in contact with you regarding your magic is affected.

Nature (druid, ranger, monk) 

Druids and rangers gather the magic of nature within themselves, then manifest it as needed. Monks who cast spells can do so thanks to meditation which centers the monk’s mind on their place in the natural order. 
For Players. The DM will be in contact with you regarding your magic is affected.

Patron-Granted (warlock) 

A warlock’s magic is dependent on the Arcana of their patron’s home world. Like clerics, warlocks hold any spellcasting power within themselves, rather than manifesting it from the Arcana in the moment. Because a patron is not tied to the makeup of any particular world, a warlock’s magic is not affected by preparing or casting outside their home world.