The moment you start a sequel, you have to ask yourself what elements from the original game should make a return. The first thing to be examined were the enemies:
Some of the basic movement patterns still made sense, especially for the earlier areas of the game where players were getting used to things. But for more challenging enemies, the patterns would need to be a bit more complex. Difficulty balance is a tricky thing. What might seem like a trivial addition to an enemy might actually play very differently than what you expect. This is made more complex when you mix and match enemy types. I tried to initially make small differences between enemy types so that while each area would have new monsters to slay, they would bring some familiar behavior from a previous area.
For example, movement patterns could start out as simple straight lines. But then the straight lines could change to incorporate pauses and bounces. Sure, a bouncing enemy on its own might seem like a similar threat to an enemy that moves in a straight line. But pair it with an enemy that shoots a projectile and you suddenly have to worry about jumping a little more.
Many of these patterns developed as the game was created. It is difficult to know what patterns will offer enough challenge without being too much. And in many cases, an enemy that was designed for one area with a specific look would get redesigned for another area if they didn’t fit the difficulty curve they were planned for. So many of the advanced enemy behaviors I had planned felt too difficult once I had them in the game, and they would get pushed into later and later areas. Sadly, I should have worked with much simpler art in the beginning so I could rearrange these behaviors in a more modular way. But when you design, for example, an undead enemy you had planned for a Graveyard, but then find their behavior would work better in a later swamp area, you have to rethink the enemy to fit the swamp theme.
On the whole, I think the world of Slayin has a distinct cast of monsters. I worked very hard on giving them a place in their world. Each location was built to offer a new challenge. And with all the unused creatures, Slayin 3 will definitely have a pile of ideas to build on. 😉