Yu-Gi-Oh: 10 Most Powerful Unbanned Cards In The Game
4. Jet Synchron
Jet Synchron is a level 1 tuner monster with 500 attack and 0 defence that allows you to discard one card from your hand to return it from your graveyard to play. The common play is to synchro him away and revive him using its effect ready for another summon.
The real problem with this card is since Crystron Halqifibrax became legal it's super easy to abuse and combo off with Jet Synchron and make unbreakable boards, first turn kills or essentially make it so your opponent can't play.
Jet Synchron promotes this unhealthy, solitaire style of YuGiOh play where you can play through any hand trap or form of interaction your opponent may have and allows you to do what you want in terms of special summoning monsters your deck normally wouldn't be able to have access to. 100% should be on the ban list.