Changestones

You place up to 10 specially prepared stones on the ground and speak a command to conclude the casting of the spell. The stones become the guardians of a designated area within range that is no larger than a 20-foot cube. When you cast the spell, you can designate creatures that won't awaken the guardians. If a Tiny or larger creature touches or enters the warded area before the spell ends, the stones transform into creatures that look and fight just like Mud Mephits that have been affected with a Bless spell. This bless effect can't be dispelled. 

These stone-born mephits are always at maximum Hit Points when created (42 Hit Points each) and do not speak any language. During combat, the mephits won't willingly move father than 100 feet from the warded area. 

When reduced to 0 Hit Points, a mephit explodes in a burst of sticky mud, and the prepared stone used to create it is destroyed. Otherwise, the mephits revert to prepared stones when the duration of the spells expires, and the stones can be used as the material components for another casting of the spell. 

Using a Higher-Level Spell Slot.  If you use a spell slot of 7th level or higher, the duration is 7 days. If you use a spell slot of 8th level or higher, the duration is 30 days. If you use a 9th level spell slot, the spell lasts until it is dispelled. 

Adapted from a Dragon Magazine spell