Ability Score Increases
The ability scores seem moderately well-balanced, if a bit on the underwhelming side. Less powerful than those of a half-elf (+2 Charisma, +1 to two other abilities) and a little better than the variant human (+1 to two scores),the human gets a feat while Voidtouched gets access to some spells.
The ability scores are underwhelming because they don't synergize well. Although Triton's get a +1 to Strength, Constitution and Charisma. These synergize well together. A Paladins uses Strength for attacking, Constitution for HP, and Charisma for spell casting. As no class uses both Intelligence and Wisdom, you're effectively throwing away one skill and the two skills you utilize will be at a lower tier than everyone else(+1, +1 instead of +2, +1.)
Size
Should be the size of being before it was exposed to the Void.
Speed
Should be the speed of the of the being before it was exposed to the Void.
Darkvision
This darkvision has a radius of 120 feet, while most races have a radius of 60 feet. Should probably changed thusly.
Telepathy
This is very comparable to the Great Old One warlock's Awakened Mind feature. Awakened Mind requires that the recipient understand a language.
Memory of Madness
Resistance to psychic damage is very similar to Tieflings' fire resistance, but instead it covers a less common damage type.
Immunity to Modify Memory. This is fine. It's immunity to a single spell and makes sense based on the race.
Magic of Madness/Voidtouched Psionics
You have the ability to cast Mage Hand and make it invisible. The Arcane Trickster Rogue can do exactly this. I don't feel like this takes away from the Arcane Trickster, as the purpose appears to be telekinesis.
At 3rd Level you can cast Chaos Bolt once per short rest. Chaos bolt does 2d8+1d6 damage, with a with a 12.5% chance of bouncing to another target. The closest equivalent to this is the Tiefling's ability to cast Hellish Rebuke (2nd Level). This does 3d10 damage and can only be used as a reaction, not as an action. Chaos Bolt does. As stated by other people, this should be only be cast at first level.
While it's balanced, I don't feel like Chaos bolt fits in with the theme of the race.
At 5th level, you can cast Detect Thoughts once per long rest. The equivalent of this would be the Tiefling's ability to cast Darkness once per long rest. Both spells are 2nd level, though Darkness is more combat-oriented than Detect Thoughts.
Detect Thoughts is a much better fit than Chaos Bolt for this race.
Conclusion
I'm conflicted on the overall feel of the race. Structurally, it's very similar to Tiefling. Mechanically, I can see this being a very good race for interrogations, subterfuge, and reconnaissance. However, most if not all of the features in this race can be obtained as a warlock. The race kind of feels like a warlock; however, the ability scores wouldn't be good for a warlock. It also feels like a mystic, with the telepathic and telekinetic abilities.
There's no real unbalance to this race. However, I can't really figure out what this would be good for. I feel like it would be improved by adjusting the ability score bonuses (maybe retaining the bonuses of the creature of the creature's original race, and giving a penalty to wisdom to simulate insanity).
This is a very good start. It just needs some tweaking to improve the overall feel of the race.
