Haunter’s fantastic offensive stats, along with its access to solid STAB moves in Sludge Wave and Hex, made it a huge threat in Gen 6 NFE. Its access to utility options such as Will-O-Wisp and Pain Split more than made up for its poor defenses. More specifically, Haunter fit the definition of broken as stated by Smogon’s Tiering Policy. Its incredible offensive STAB coverage meant there was little capable of switching into its attacks. Will-O-Wisp crippled physical threats and walls with increased chip damage and boosted Hex damage, letting it break through bulky walls easier. On top of this, removing Haunter from the game was very difficult. With no Z-moves, Haunter could easily run Eviolite or Colbur Berry. Depending on the 4th moveslot, Haunter was capable of walling or creating a 50/50 scenario where it could beat all its counters and Pursuit trappers. Munchlax was walled by Pain Split sets. Neither Pawniard nor Krokorok appreciated switching into Will-O-Wisp and, if the Haunter had an Eviolite or Colbur Berry, Scarf sets couldn't even reliably trap it if it carried Hidden Power Fighting as its 4th move. It was incredibly difficult to prepare for in teambuilder and any team with Haunter had a significant advantage against any team without it. It heavily limited teambuilding and it was so good, its usage and inclusion on teams felt mandatory. Overall, Haunter’s raw damage output coupled with its versatility and few possible counters, including the loss of its best counter in USM NFE in Alolan Grimer, resulted in its ban.