UngeheuerLich
Legend
Maybe the easiest way is allowing the assassin go on initiative 20 because he got the drop on the enemy. There does not need an ability check if the situation is clear.
And as I said earlier: RAW the rogue can start combat again and again until the initiative order favours him. He does not have to unhide... It is a terribly complicated situation... The rules are very clear and there is no question about who can be attacked with auto crit and who can be attacked with advantage.
On the other hand: it is also quite clear that the rogue does not really have to be faster against someone who was surprised but has beaten the rogue's initiative. Since surprising necessarily means the rogue is still hidden, he still has advantage on the attack roll. No matter when his turn in the initiative order is. So in this case we talk about a theoretical case. It may be relevant for a melee rogue who runs up to the enemy, but assassinate is most probably something you do at range. If you jump put of cover and attack alone, hoping to assassinate someone... maybe better be another kind of assasin. Use poison that makes the enemy sluggish or so. Or be really fast in the initiative order.
And as I said earlier: RAW the rogue can start combat again and again until the initiative order favours him. He does not have to unhide... It is a terribly complicated situation... The rules are very clear and there is no question about who can be attacked with auto crit and who can be attacked with advantage.
On the other hand: it is also quite clear that the rogue does not really have to be faster against someone who was surprised but has beaten the rogue's initiative. Since surprising necessarily means the rogue is still hidden, he still has advantage on the attack roll. No matter when his turn in the initiative order is. So in this case we talk about a theoretical case. It may be relevant for a melee rogue who runs up to the enemy, but assassinate is most probably something you do at range. If you jump put of cover and attack alone, hoping to assassinate someone... maybe better be another kind of assasin. Use poison that makes the enemy sluggish or so. Or be really fast in the initiative order.