'You' and 'your' in card text refers to the player. For example, Sparkmage cares about 'spells you've cast,' which includes any spells from any of your spellcasters. As another example, Bone Rabble would trigger if you used your Avatar's ability or if you used Frontier Settlers. Some older cards use the word 'you' to mean 'your avatar.' If it's impossible to read the card as 'player' in a sensible way, then use 'avatar' instead. For example, Cerberus in Chains follows your avatar and Avatar of Earth looks at her own adjacent sites.