if you feel bosses difficult.
try this:
select Patchouli,
select the earth sign,
walk to somewhere you like ,then hold Z(jump) to float,
press (not hold) X (shot) to put an amulet in front,
walk in the amulet,
press S to select the fire sign,
hold X to shot for a few seconds,
press A to select the earth sign and go on,
you can beat most bosses like this.
Tenshi and Raiko's survival card are difficult,though.