Bigby's Thinking Rune

Bigby found this spell while adventuring giant's lands and used it to gain advantage on him and to override the large power rift between a gnome and a giant. He discovered it while he and Mordenkainen were adventuring and watched giants use their magic. Bigby later realized that he did not have the capacity to cast some of their spells while Mordenkainen (as a member of the Wizards Three) could cast each individual spell. Bigby was not mad per se at Modenkainen, but he did want an upper "hand" on magic that he had watched for far longer than his human friend. The gnome decided to mix together the best spells he saw the giants cast and had Mordenkainen work on mixing them together. After the spell was invented, Bigby realized that to channel giant magic he needed a rune. As a result he travelled far and wide, begging giants for a rune that would work, but none would accept since no giant would teach a gnome. Eventually, Bigby got so annoyed that he used his contacts (deities and such) to trap the soul of an up and coming giant teacher within a stone. The giant's soul manifested into a new rune that would carry it's soul once carved. Bigby realized the sentience of the giant would allow him to use this unique rune more than once. He later would write the spell down on a scroll, symbol and all, and send it down to a small library hidden in the trees, wizards still copy down this spell today...

You carve a half T rune with a golden dot under the horizontal line onto a stone or wood piece. Once you finish carving, the stone or wood will liquify and evaporate into a purple rotating symbol floating in front of your left hand. If you open your palm in the direction of an enemy, the rune will fly at the enemy, crackling with lightning. The second the rune hit's the creature, it must make an Intelligence saving throw. If the creature fails, the sentient mind of the caster is implanted into the enemy's thoughts, allowing the caster to influence the enemy. If the creature  is killed, the spell ends. The spell does not end until five "command thoughts" (influencing and powerful thoughts) are planted. If the creature succeeds it's saving throw, it catches the rune and gains advantage on all Charisma (Persuasion) and (Intelligence) Insight checks and saving throws. You can not cast thoughts that involve any violence, if you try the spell, the spell ends and the effects of the creature succeeding come into play. The thoughts are forgotten after 2 turns. You also can not effect creatures that cannot be charmed.

Aberrations are immune to this spell and the spell with bounce off of them, ricocheting towards the caster. In particular, mind flayers can also make a Charisma (Persuasion) check for an extra command thought.

The only race that can recognize this spell are Giants, (Frost, Hill, Stone, and Storm) so they are the only ones that will know if they were  charmed.

At higher levels:

At level nine, the caster has the choice to make a Charisma (Persuasion) check to possess the creature's mind for 5 minutes (all magic jar rules apply). You can also use the check to charm the creature at level 12. At level 20, the spell will add a 5d6 psychic damage after being charmed or possessed.