Every area of Slayin 2 has a boss, but the sheer number of areas meant that coming up with lots of interesting bosses was going to be a challenge. Early on, Mega Man style bosses were used as inspiration for the basic boss AI. The bosses needed to become more nimble and reactive to the player as the game got harder. And the dual plane system meant that the bosses had to deal with players who jumped planes often.
This has lead to a lot of boss revision as the game has developed. Bosses evolved to have “multi plane” attacks as well as some attacks that force the player to switch planes in order to avoid damage. In rare cases, the second plane is removed entirely, forcing the player to deal with the boss more directly.
