The counter for the Incense Burner is maintained between combats. As such, it is worthwhile to plan out the last combat before a boss fight and end that combat on a turn such that you become Intangible on a turn that the boss will surely attack. For example, ending the last combat in Act 1 when the Incense Burner reads 3 ensures that you will become Intangible on the turn that Slime Boss uses Slam.
Here are the numbers to block a boss' big attack by ending your previous fight when the counter reads a specific number:
Intangible every 6 turns.
