Building an assassin elf in D&D is like crafting a shadow with a heartbeat—silent, lethal, and eerily beautiful. I'd start with a Wood Elf for their 'Mask of the Wild' trait, letting you hide even in light natural obscurement. Pair that with the Assassin rogue subclass for those brutal surprise attacks. Sneak Attack becomes your best friend; imagine slipping behind an enemy, dagger glinting, and dealing 6d6 damage before they even blink.
For stats, prioritize Dexterity (stealth, finesse weapons) and Charisma (disguises, deception). Take the 'Skulker' feat to vanish in dim light, and maybe 'Elven Accuracy' for triple advantage on attacks. Background? Criminal or Spy, obviously. And don’t forget poisons—basic dagger scratches are boring. Dip your blades in wyvern venom and watch the chaos unfold. Honestly, playing this character feels like orchestrating a deadly ballet.