Once Hazards #6 has been completed, here are some more ideas for hazards.
[ ] Log Bridge
Since water slows the player a hazard/anti-hazard could be a log that goes across water. While walking on it the player is immune to slow down. However, the log pushes the player to a side if the player is not walking dead center.
[ ] Trip Wire
Apparently tripwires with bells attached were used as one countermeasure against ninjas. So maybe a pile of leaves hides the tripwire and when walked on will trigger noise and a volley of arrows rains down on a quarter of the map. An easy first pass on this could be a pile of leaves that when walked on does damage to everything in some radius around the leaves after some amount of seconds.
[ ] Spike Trap
Some hidden trap door that after a moment of pressure will open to a spike pit. Basically, if the player collides with the collider for X amount of time, a spike pit animation will come out of the ground dealing a high amount of damage to the player.
Once Hazards #6 has been completed, here are some more ideas for hazards.
[ ] Log Bridge
[ ] Trip Wire
[ ] Spike Trap