Inviting Ambrus is useful, but you don’t have to invite him to get Scarlet Shield.
If you invite him, Ambrus stays with Coen and you will hear him speak at different points later in the game.
Leaving him behind gives you a different outcome, and the choice can also matter again much later in the story.
What Happens If You Invite Ambrus?
Ambrus becomes a presence inside Coen.
You will occasionally hear him comment on what is happening as you continue through the game. This gives you more dialogue from Ambrus and some extra context during later events.
The decision can also come back into play near the end of the game, so it isn’t completely forgotten after you leave Anachora.
Do You Need to Invite Ambrus to Get Scarlet Shield?
No.
Scarlet Shield is tied to Ambrus’ blood, not the decision to invite him.
If you reach the invitation choice after drinking his blood, refusing Ambrus does not suddenly remove Scarlet Shield.
So don’t choose Invite just because you’re worried about losing the ability.
Is It Better to Invite Ambrus?
If you’re mainly worried about gameplay consequences, inviting him is a reasonable choice.
You get to keep Ambrus around for additional dialogue, and his presence can affect something later in the game.
But this is also a story choice. If you don’t want Coen to carry Ambrus with him after defeating him, you can leave him behind instead.
Does This Choice Change Corruption?
The invitation itself does not appear to add Corruption.
The important distinction is that drinking Ambrus’ blood and inviting Ambrus are two separate decisions.
So if you see your Corruption change around this part of the game, don’t assume that choosing Invite itself is what caused it.
Quick Answer
You can invite Ambrus, and there are reasons to do it, but you don’t need to invite him to keep Scarlet Shield.
Inviting him allows Ambrus to remain with Coen and adds more of him to the rest of your playthrough. The decision can also matter again later.
If your only concern is losing Scarlet Shield, though, you don’t need to worry about that when choosing whether to invite him.
