I honestly think the once per turn limiter is a healthy one to have regardless. Getting multiple shots at it in one turn moves in the "unfun" territory, IMO.
ELABORATE DEATH TRAP 14
Once per turn, after an enemy ends a move of 1+ spaces within 4 clear spaces of Doctor Doom, you may roll a d20. On a 14+, place that enemy within 4 spaces of Doctor Doom and end the turn. If that enemy is placed adjacent to Doctor Doom, it takes 1 wound.
This.I trust you guys. This is the version to go with then?
ELABORATE DEATH TRAP 14
Once perturnactivation, after an enemy ends a move of 1+ spaces within 4 clear spaces of Doctor Doom, you may roll a d20. On a 14+, place that enemy within 4 spaces of Doctor Doom and end the turn. If that enemy is placed adjacent to Doctor Doom, it takes 1 wound.