Bone cage

You leave a mark on a skeleton you can touch

When you detonate the mark the ribs of the skeleton (undead ) extend to capture the creature within 5ft of it 

When you detonate the mark the (undead) becomes inactive for the duration 

instead of taking the attack action you can detonate the mark 

All creatures within 5 ft of the detonated mark must succeed a dexterity check (spell save DC) or be trapped (grappled) for the duration 

If caught the creature can escape by succeeding a strength check (spell save DC)

You can burry your marked skeleton (or undead) to create an laying trap 

The activation condition is a creature that steps on it 

(Add +1 to the str and dex check if the undead was burried)