Here is the full list of all 25 Solar 2 achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
What is the entity?
Make a 6 star system.
As a star have an orbiting life planet with 100 kills.
Have 15 asteroid moons around your planet.
Get the maximum possible life in your system.
Get 10 planets in your system orbiting clockwise.
Grow to a black hole from a multi star system.
Go from a small black hole (<150k mass) to Big Crunch without the interface visible.
Go from Big Bang to Big Crunch in under 20 minutes. No menu respawning.
Complete the 2nd part of the "Fine Art" mission without dying and without evolved life on your planet.
Complete each of the "Assassin" mission parts without dying.
Kill all the attacking ships in the first part of the "Heist" mission before completing it.
Start the 3rd part of the "Duel" mission as a single star with no planets and beat it in under 3 minutes.
Complete the first part of the "Concert" mission in under 1 minute.
Complete the second part of the "Concert" mission with no evolved life on your planet.
Why?
Get Lost.
Make a 40 star system.
Beat all the missions without using Physics or God options.
Beat the final boss as a dark matter star without using Physics or God options.
Steal 10 planets on the "Planet Stealer" challenge mission.
Complete every challenge mission with any score.
Complete every challenge mission with a hard level score.
Get 4 points in the star challenge mission "Snowball Fight".
Grow so large you absorb the whole universe.