How to Plant Land Mines in D&D 5e

[Eltab]

Explosive Runes on a table, light tablecloth on the tabletop, Necklace of Fireballs on the tablecloth. The Necklace is set to go off when they take damage.

 

[Skywatch]

Harzel, the glyphs can be set to trigger when they move x amount of feat from the point that they were cast, and Dausuul, the zombie with the bag of coppers is so you don’t lose spells because the rules of spellcasting say that the affect of 2+ spells with the same name don’t overlap, you only use one

 

[Yunru]

Guys, guys, guys.
True Polymorph is the answer.

Pressure pad "kills" object. Object reverts.

 

[Skywatch]

Into a continent from the plane of elemental earth. I have no idea how you got that stuff.