I've survived up to 30 waves, with my second highest score being 28 waves. fun game, i enjoy how fast paced it is and how quickly the upgrade screen moves so that i can spend more time in what's fun.
As I played I noticed that the blood penalty for completing a dash is heavily felt, especially in the earlier rounds where there are less blood pickups per wave. As a result, I found it best to generate as much blood as possible (killing enemies and spawning more) before a dash is necessitated due to my blood running out; This way I could offset the amount of blood I lost by dashing with (hopefully) the large amount of blood gained by dashing. For me, this meant minimizing dashing as much as possible in the earlier rounds, until about round 10 or so at which point I could more actively enjoy the process of shooting and dashing into blood pick-ups.
At around the beginning of round 26 and onward, I feel that the beginning of the round is the most difficult, before leveling off as the round continues.
The blood bar depleting at the start of a round, even before enemies spawn, combined with the already rapid depletion of the blood-bar in higher rounds creates a spike in difficulty simply because there's less blood to manage before the player can take any meaningful action to offset that depletion.
This spike in difficulty balances out as the round continues however, due to the amount of blood pick-ups which linger in-between spawns of enemies and from the upgrade 'More Blood Drops'.
I had a lot of fun playing this for the hour that I did, and I especially enjoyed the sound effects and music!