Another Gem on this jam, I gave it a decent rating.
Now let me bring some suggestions to improve the game further :)
1) First of all, [Sanity] status has no effect on the gameplay and no sense in raising its MAX amount. I would like to suggest to make it decrease not by having the maximal Knowledge, but as long as the creature is summoned. With this, more powerful creatures will increase your Knowledge fast, but you should increase the Sanity amount and take the pauses to regenerate Sanity to do not run out of it too fast.
2) Next, judging from the stated above - zero Sanity would result to Game Over.
3) Increase the Sanity consumption a bit. 1|2|3|5|8|10|12|15 will be perfectly fine - less consumption for starting creatures, more for Cthulhu.
4) Actually, there is no need to increase the max Sanity by +10 when the new Creature is unlocked. Let it stay the same. However, if the increase was intended by game design, raise this amount to +20, because +10 is really low and has no any noticeable effect.
5) Give us a Goal to achieve. An ultimate Grimoire for 150.000 Knowledge, "The Soul of The World" in English, or "Anima Mundi" in Latin language. Purchasing this Book lets us Win the Game.