{Beacon of Immortality}, {Tainted Remedy}.
Instakill?
{Rain of Gore} won't work unless they cast it. Thanks Remillo
Remedy, yes, Rain, no.
Rain specifically says that they have to be the controller of the spell or ability. If You could somehow Hive Mind Beacon and make everyone target themselves, then that'd work.
Really thinking about a {Tainted Remedy} modern deck...
But with target player gains life tools you could outlast them. Except twin/insertotherdecksthardintcareaboutlifetotals but there are ways to deal with that.