The alternate multiclassing in Pathfinder Unchained was based on feats, and you had to take one at first level. One of the options was sorcerer which comes with a bloodline (like infernal). The abilities that go with it don't come until the later feats you get every four levels or so.
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Sorcerer
A character who chooses sorcerer as her secondary class gains the following secondary class features.
Bloodline: At 1st level, she must select a sorcerer bloodline. She treats her character level as her effective sorcerer level for all bloodline powers.
Bloodline Power: At 3rd level, she gains her bloodline's 1st-level bloodline power.
Improved Bloodline Power: At 7th level, she gains her bloodline's 3rd-level bloodline power
Blood Feat: At 11th level, she gains one of her bloodline's feats or Eschew Materials.
Greater Bloodline Power: At 15th level, she gains her bloodline's 9th-level bloodline power.
True Bloodline Power: At 19th level, she gains her bloodline's 15th-level bloodline power.
Infernal Bloodline – d20PFSRD
