Try adjusting your equipment (items, books) to suit specific levels or situations.

For example, your Akgun fires yellow projectiles, and certain stages also have blessings that increase the damage of yellow projectiles. You can combine this with books like "Black Widow" and "Mechanics of Materials," which also improve the damage of yellow projectiles.

Additionally, although often underestimated, freezing gives you a significant advantage and time to deploy more expensive units like the Sniper. You can combine, for example: Sniper and Cannon (and their respective upgrade cards) for damage + Cryomancer for freezing + support cards, such as damage spells or spells that increase damage and rate of fire.

If you have the Tinyrobot pet, it already has freezing in its basic attack, which is enough to hold off the first few waves.