We already have fiend blooded sorcerers how about one with some true power?
Child of Merlin
Many tales tell of a powerful magic user who offered wisdom to kings and guided bloodlines for centuries. Few remember that this person was a child of the most powerful devil. Merlin was a powerful man, but his diabolical heritage passes threw his bloodline to all his children and his lust for power and women meant that he has children across the multiverse. You are one of those children whose spark has awoken and now you manifest all the awesome powers that master magician with devil blood can bear!
Guide of kings
At 1st level, Merlin’s ability to guide others emerges in your. You gain the bardic inspiration ability of a bard of your level. You can use this a number of times per day equal to your Charisma modifier.
Wild Man of the Woods and Hells
Starting at 6th level, Merlin’s shape changing abilities manifest in you. You gain the wild shape ability of a druid of your level. As an added bonus, you can choose to change your shape into an animal or a fiend following the same CR restrictions as a a druid of your level.
Master Communicator and Shapeshifter
At 14th level, you gain the ability to change your shape as you see fit to match any occasion. You can cast polymorph on your self twice per day. Furthermore, you gain the permanent effect of the tongues spell to talk with all creatures who understand language.
Your Patriarchs Powers and Weaknesses
Beginning at 18th level, you gain the faults of your patriarch, but also gain a larger portion of his powers. You gain disadvantage on all saves vs any effect that causes the Charmed condition, cause psychic damage, or control your mind, but you also gain advantage on all other saving throws. You gain resistance to all other damage, but gain vulnerability vs all bludgeoning damage. For these effects and damages, apply worse penalty if multiple effects or damage types are mixed together.
Let’s get back to the giant archetypes with the Giant Bloodline for the DnD 5e Sorcerer.
Giants are brutish creatures that don’t always kill those they capture. Or some seek them out to live among them in the wilderness. In either case, some children emerge from unions that may occur in the wilderness. You are one of these children. Your magic power emerged early as your giant heritage began to take hold.
Giant blood flows through your veins making you tougher than most. At 1st level, increase your Constitution or Strength by 3, to a maximum of 20.
Starting at 6th level you become increasingly aggressive. When you cast a cantrip you may also make a strength-based melee or thrown weapon ranged attack as part of the same action.
Muscle Mass Growth
At 14th level, your body continues to inherit more of your giant ancestral traits. You gain a +3 to Strength or Constitution, to a maximum of 20.
Beginning at 18th level, you grow into the giant you were always meant to be. Increase your size to one category larger and change all your hit dice to d12s and recalculate your hit points.
How about a completely different way to cast spells as a Sorcerer in 5e?
Magic is in your blood….., and in blood in general. Life is power, and you know how to extract power from your own life.
Power in the blood
You no longer have a Sorcery Points pool, but you add any point you would gain as hit points. You also no longer have a limit to the number of spells you can cast per day. When you cast a spell of any level, lose double the spell level in hit points. You can cast spells as long you still have positive, non-zero hit points, but you must take the damage. Cantrips cause one hit-point loss.
Spilled blood, released power
Starting at 6th level, when you are dealt damage as a reaction you can use that hit point loss to cast one spell as a reaction. The spell level must be less then or equal to double the lost hit point total. You do not take damage for casting this spell. You can not use this ability again until you take a short or long rest.
Starting at 14th, another can donate a small vial of blood to you. Another creature can take any amount of damage and donate that damage to you as hit points you can use to cast spells. A creature can take up to 30 point of damage. You can use these points of damage as you would normally use hit point for Power in the Blood. This donation of blood is usable until that creature takes a long rest.
Starting at 18 level, you can now use the suffering of your targets to energize your spells. As a swift action on your turn, when you cause damage to a creature using one of your spells, you can capture up to double your level in hit points of damage from that creature. You can use these points of damage as you would normally use hit point for Power in the Blood. You must use these points within an hour. Or, the power leaves them, and they are lost. You can not use this power until you take another long rest.