Bosses
Every 10th level spawns a boss with a 30-second timer. Beat it to push into the next wave; if it escapes, you retry the current wave (your Essence & upgrades stay).
Dodges
From Level 25, a spirit may wind up an attack you can't tap through — a spinning circle shows a direction. Draw a circle that way with your finger to dodge it.
Shields
From Level 50, some spirits raise a shield that neither tapping nor idle damage breaks. Swipe the way the arrow points to shatter it — a swipe is the only way through.
Parries
From Level 75, a spirit may wind up a heavy blow you can't tap through — hold your finger down to fill the ring, and when it's full you brace the hit. A boss throws one defensive beat per fight — a dodge, shield or parry — with its timer still running, so be quick.