I think that all the rares should be removed from timers and instead replaced with a % chance of spawning in place of a particular mob. ie. shadow dragon rather then regular dragon (yes i realize this is just a hue spawn of the same mob, but I sure it can be coded to spawn an entirely different mob in place of another one)
So you could go with replacing a particular dread spider with a beetle on a small % chance or make it even more fun and have it so any dread spider can spawn as a beetle and reduce the spawn chance even lower.
This could be done for all rare mobs making farming a particular area part of getting a rare pet (ie, the wolf campers) and no just jumping in exactly X hours from the time the last nightmare was tamed. I dont really see any drawbacks here at the right (low) chance of spawning rares stay rare and farming (certain) mobs can be hit with a nice big surprise.
So you could go with replacing a particular dread spider with a beetle on a small % chance or make it even more fun and have it so any dread spider can spawn as a beetle and reduce the spawn chance even lower.
This could be done for all rare mobs making farming a particular area part of getting a rare pet (ie, the wolf campers) and no just jumping in exactly X hours from the time the last nightmare was tamed. I dont really see any drawbacks here at the right (low) chance of spawning rares stay rare and farming (certain) mobs can be hit with a nice big surprise.