Blue Magic

A learned Blue Magic Sorcerer stands among his comrades as they fell a powerful Djinni. With a brief moment of concentration, he understands how the elemental was able to walk on the clouds using the Wind Walk spell and quickly memorizes the patterns and its functions. A multiclass Blue Magic Beast Master strides beside his animal companion dual scimitars drawn, as they stalk the Barghest's lair for the opportunity to learn its potent innate stealth magics. 

Due to your strong ties to magic, you can see it.  Your training has honed this ability to emulate the intricate patterns that are created during a creatures Innate Spellcasting.  Much like a savant musician playing a song after hearing it for the first time, you are able to see and memorize these enemy spell patterns for later use.

Spell Versatility(enhances Spellcasting)

Whenever you finish a long rest, you can replace one spell you learned from this Spellcasting feature with another spell from the sorcerer spell list. The new spell must be the same level as the spell you replace.

Blue Magic

Beginning at 1st level, you have turned your ability to sense patterns in the weave, into the ability to mimic them.

Spell Learning:  You must first witness an enemy creature cast an Innate Spellcasting spell in battle.  Once the creature is defeated, you can make a Concentration check for the chance to add the spell to your sorcerer spell list.

Spell Learning DC = 10 + the innate spell's level.

You do not have to be hit by the spell, but you must have the appropriate level spell slot to be able to learn it.  If you are incapacitated when the enemy is defeated, you do not get an opportunity to learn the spell. Any spell you learn this way is considered a sorcerer spell for you, and you are able to use any weapon you are proficient with as a spellcasting focus for your sorcerer spells.

At 2nd level, a Blue Magic sorcerer's body is so steeped in the weave that any spell learned this way, of any level, can be cast using sorcery points instead of spell slots. This feature follows and expands upon the table from the Sorcerer class feature, Font of Magic. Spells of 6th level cost 8 points, 7th level cost 9 points, 8th level cost 10 points, and 9th level spells cost 12 sorcery points.

Mighty Guard

By 6th level, you have learned to weave your magic to fortify yourself against harm. When you are hit by an attack or you fail a saving throw, you can use your reaction to gain a +3 bonus to your AC against that attack or a +5 bonus to that saving throw. 

When you use this feature, you can’t cast spells other than cantrips until the end of your next turn.

After reaching 14th level, you gain the ability to use this feature on an allies within 5 feet of you.

Bad Breath

When you reach 14th level, you learn the Contagion spell, which doesn’t count against your number of sorcerer spells known. In addition, you can cast it by spending 7 sorcery points or by expending a spell slot. If you cast it using sorcery points, it is a ranged spell attack with its range being a 15-foot cone instead of touch.

After reaching 18th level, you gain the ability to choose two diseases to infect the targets with when casting this spell using sorcery points.

White Wind

At 18th level,  you no longer need to use your bonus action to create spell slots with sorcery points, or vice versa.

Also, you learn the Mass Healing Word spell, which doesn’t count against your number of sorcerer spells known.  You can cast it by spending sorcery points or by expending a spell slot.  If you spend sorcery points to cast the spell at 5th level or higher, the creatures healed can also end either one disease or one condition afflicting it. The condition can be blinded, deafened, paralyzed, or poisoned.