Can this Fighter/Assassin build and setup allow 2 assassinate auto critical sneak attacks on round 1?

Question

Suppose I'm playing in combat as a 2nd level fighter/3rd level rogue assassin, and at least one more party member surprises the enemy. We have higher initiative.

Can the assassin use his action to score the autocritical + sneak attack, and then use the fighter's action surge feature to use a ready action to repeat attack against the same target, triggered on some action taken by his other party member?

Answer 1

Yes, this is legal

As long as you hit with both attacks -- the one on your turn and the one on your ally's -- you can autocrit with Sneak Attack damage on both. All the requirements of Sneak Attack and Assassinate are fulfilled.

Other builds that can do this

These MC builds achieve the same thing at a later level, but here's to illustrate that you can do this without Action Surge, using just your regular Action.

• A Sorcerer 3/Rogue Assassin 3 with Quickened Spell

  • Quicken Green Flame Blade or Booming Blade (GFB/BB) for a bonus action, and then use their action to Ready another GFB/BB

• A Wizard 5/Rogue 3, or Sorc 5/Rogue 3, or Lore Bard 6/Rogue 3

  • Pre-cast haste to receive an extra action before the surprise round begins. During the surprise round, use that extra action to make a regular Attack, and use your regular action to Ready a second regular attack (you may not ready a spell as Readying a spell requires Concentration, which haste already takes up)

• A Frenzy Barb 3/Rogue 3, Strength-based

  • Use Frenzied Rage as a bonus before the ambush, and during the surprise round, use their bonus action to make one weapon attack. They can use their action to Ready another attack.