Melee
Bonus action: The Hound that attacks the enemy with advantage (pack tatics) and flanking and DC 13 for prone. 10average damage
Move 15 fts. ......Remember that It has advantage with pack tatics and flanking add +2 on attack roll.
The hound does not have advantage because it is in darkness and can't see. That cancels the advantage.
Also Flanking does not add +2. If you use the optional flanking rules it grants advantage which the hound can not get due to being blinded.
Remember that one disadvantage cancels all advantages. So if the hound is attacking a prone (advantage), flanked (advantage), pack tactics (advantage), while unseen (advantage) but the hound can't see the enemy himself (disadvantage) ...... That makes it a straight up roll without advantage or disadvantage.
Finally, even though he is in darkness the enemy can attack the hound without disadvantage and if he readies an action he can attack your horse without disadvantage. Even from the prone position, he can make these attacks without disadvantage as the horse and the hound can not see him.
..... the Hound's Oportunity attack that can prone him).
Bonus action: Quicken Empowered triple advantage Scorching Ray for average 34 damage
It is not possible to get advantage on the quickened scorching ray if they enemy is prone. Being prone imposes disadvantage on attacks from greater than 5 feet away and using a ranged attack from closer than 5 feet also causes disadvantage. This means no matter what you do, you can't get advantage on scorching ray if the enemy is prone.
If you use scorching ray from outside 5 feet the disadvantage for being prone cancels the advantage for being unseen.
If you use scorching ray from inside 5 feet, the disadvantage for using a ranged attack with an enemy within 5 feet cancels the advantage for prone and the advantage for being unseen.
Now if you cast fireball with the hound next to him, then yes he would have disadvantage on the save.
Invisibility Spell +7 Stealth check with Sorcerer's Magical Guidance (Better than Advantage) and Darkvision 120ft.
All enemies see 60ft on darkness, but the Shadow Sorcerer see 120ft. So, you have triple advantage against enemies that can't see you.
It's a reliable Stealth Character and really effective on natural darkness.
Level 8, get feat for Expertise on Stealth checks. It's an insane +12 Stealth Check, with Sorcerer's Magical Guidance, It's still more insane.
It's a scary character.
I don't know how you get to +12 stealth at level 8. With expertise and a 20 dexterity it is +11, that is the maximum you could have by level 8 and to do that with point buy you would have needed to start with a 17 or 18 Dexterity and take a dedxterity ASI at level 4.
A 11th-level Rogue is going to routinely have a +13 stealth, and he can't possibly roll lower than a 10 which means the minimum he can possibly roll is 23. If he rolls two natural 1s with disadvantage his stealth roll is still 23! That is without using any spell or sorcery points at all. The average stealth roll for that Rogue will be
26 and that is with
no feat, no spell and no magical guidance boost. He can do that all day long. It can't be lower than 23, so even if you put the Rogue at disadvantage on the roll the average only drops to 24.
If your 11th level sorcerer has a 16 dexterity and you have expertise in stealth from a feat and are running invisibility and you burn sorcery points for magical guidance you will average 27, only 1 point better using a 2nd level spell slot and a sorcery point and the downside is a lot worse if you get poor rolls.
Finally the Horse you are riding on has a 0 stealth.