Rushes in, draws a ring, bursts. Leave the ring.
It stops dead next to you and a ring snaps out on the floor around it. The ring is the blast. Everything inside it gets hit.
A cracked scarlet orb that rushes you at 0.81x your speed, which is faster than you while you shoot. Once it gets close it plants, draws a ring on the floor around itself, and 0.65 seconds later bursts into ten shards that fly out to exactly that ring and stop. Each one does 4. The burst breaks the cracker too.
It is faster than you while you shoot, so a cracker you ignore will catch you the moment you start firing at something else. Then it plants inside the pack you are already busy with, and you notice the ring too late.
Leave the ring. The ring it draws is the true reach of the burst: outside it you take nothing. A straight run out from where it planted clears it in time, but only with your thumb off the stick. Shooting, you are too slow to make it.
Or kill it during the 0.65 seconds. A cracker that dies inside the ring never bursts.
Shoot it before it arrives. It is not tough, and a cracker that dies out in the open is a cracker that never plants.
Share of everything that spawns, at four points in a run. From 1:30 one of the four new enemies is featured each minute at 2.5x its usual share, in turn.
Speeds are multiples of yours while you are not shooting. Holding fire slows you to about two thirds of that. Health grows 16% a minute, compounding, with no cap.