Previous Versions can be found here.
Termination is a Perseverance deck specific effect card which allows you to kill a monster under KR, including your own.
It's an incredibly useful card to get rid of something that's too powerful for Worsening, either due to their high HP or their ability. Most notable of this are Sans and Mad Dummy. It can also be used over Worsening on cards like MTT Fountain. Worsening deals damage which will activate MTT Fountain's ability. This card doesn't.
Since Beta 44.0, when used on a monster not under KR, it will be given KR as well as getting Paralyzed (slightly bringing back an older version of Spider Web), making it useful for a stall tactic.