From D&D Wiki
|This material is published under the OGL|
Over the course of his career, a character with a bloodline becomes more powerful than one without a bloodline. Because the power gain is gradual over a span of twenty levels, a static level adjustment doesn’t truely reflect this difference. Instead, a bloodline character must take one or more levels of “bloodline.” Class levels of “bloodline” do not increase a character’s character level the way a normal class level does, but they do provide certain benefits (see below).
If the character does not take a class level of bloodline before reaching the character level indicated on the table, he gains no further bloodline traits and must take a 20% penalty on all future XP gains. As soon as he meets the minimum bloodline level, he gains all bloodline abilities due him according to his character level, and the XP penalty no longer applies.
For example, Male Human Paladin is a 1st-level character with a major bloodline (silver dragon). The bloodline trait he receives at 1st level is a +2 bonus on Sense Motive checks. When he reaches 2nd character level, he gains the Alertness feat as a bloodline trait. Before he reaches 3rd character level, he must take a level of bloodline in order to continue gaining bloodline traits. If he reaches 3rd character level and has no bloodline levels, he does not gain the bloodline trait due him at 3rd character level (Strength +1) and must take a 20% reduction on all future XP gains. If he later meets the minimum required bloodline levels, he gains his 3rd-level trait at that time (as well as any other traits he may have failed to receive for not taking his bloodline level right away), and the XP reduction no longer applies to future gains. Before reach his 6th character level, he must have taken two levels of bloodline in order to keep gaining bloodline traits. If he takes his third bloodline level before reaching 12th character level, he becomes eligible to gain all the traits of his bloodline (as they become available when he reaches new character levels).
A bloodline level grants no increase in base attack bonus or base save bonuses, no hit points or skill points, and no class features. It counts as a normal class level (with no class skills) for the purpose of determining maximum skill ranks. Levels of bloodline never result in XP penalties for multiclass characters.
Include the character’s bloodline level when calculating any character ability based on his class levels (such as caster level for spellcasting characters, or save DCs for characters with special abilities whose DCs are based on class level). The character doesn’t gain any abilities, spells known, or spells per day from the addition of his bloodline levels, though—only the calculations of his level-based abilities are affected.
If a character has levels in two or more classes in addition to his bloodline levels, each class gains the benefit of adding the bloodline levels when calculating abilities.
For example, a 2nd-level sorcerer with a major bloodline takes a bloodline level when earns enough XP to advance in level. He is treated as a 3rd-level spellcaster for the purpose of spell durations, caster level checks, and so forth. But he doesn’t gain a 3rd-level sorcerer’s spells per day or spells known.
Similarly, the stunning attacks of a 3rd-level monk with one bloodline level have a save DC equal to 12 (10 + one-half class level) plus here Wisdom modifier, since the bloodline level is treated as if it were a monk class level when calculating the save DC. A 3rd-level monk/3rd-level sorcerer with two bloodline levels would be treated as a 5th-level spellcaster and a 5th-level monk for determining level-based abilities.