Ramses, Assassin Lord

• WOTC Official Reminder Textofficial rules
  Deathtouch — Any amount of damage this deals to a creature is enough to destroy it.

• WWizards of the Coast2022-09-09
  Official Ruling
  For the last ability to trigger, an Assassin you controlled must have attacked the player. Attacking a planeswalker the player controls won’t count.
• WWizards of the Coast2022-09-09
  Official Ruling
  Similarly, if an Assassin enters the battlefield under your control attacking a player, that creature didn’t “attack” and won’t cause this ability to trigger.
• WWizards of the Coast2022-09-09
  Official Ruling
  As long as that player was attacked this turn by an Assassin you controlled, Ramses, Assassin Lord’s last ability triggers when that player loses the game for any reason, not just due to combat damage. This is true even if the Assassin is no longer on the battlefield, no longer under your control, or no longer an Assassin at the time that player loses the game.
• WWizards of the Coast2022-09-09
  Official Ruling
  If you attack an opponent with a non-Assassin creature and that creature becomes an Assassin after attackers were declared, that player was not “attacked” this turn by an Assassin you controlled.

Rulings via Scryfall