Monster Regeneration in exchange for Rebirth Points.
A square on the path. It restores some of the Health of any injured monster as it goes over it, and has a chance of returning a teeny amount of Rebirth Points as it does so.
Called a Healing Station or Hospital or Clinic.
Could work like the Spikes and have one upgrade option for healing Health damage and another upgrade option for healing Health as a %.
It would not be very efficient for building Rebirth points, but would add to the gameplay options.