*Deleted by user*
I'm having trouble remembering the order of operations. Wouldn't Ambuscade trigger in the surprise round? So the Assassin would get their surprise attack that crits if it hits, then Ambuscade would grant another turn resulting in another attack that crits if it hits?
IIRC, Assassins gain advantage if the target hasn't acted, so they would get it there.
Ambuscade: Everyone is going to take a ranger dip. High level wizard/sorcerer + Ambuscade = unstoppable party.
Ambuscade is effectively giving you a second turn.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.
(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.