Shooting through space with invisible character

[tieren]

Here is the situation, in three consecutive spaces I have an artificer with a thunder cannon, in the next space is an invisible but not hidden firbolg, and in the third space is the bad guy.

Previous turn firbolg used hidden step to go invis, but didn't move. On artificer 's turn they take the now clear line of sight shot at bad guy.

How should I deal with the invisible PC standing right in the path of the shot?

[bid]

Assume the straight line between artificer and bad guy is a foot off the firbolg.
Assume the firbolg moved a foot to the side before going invis.
Assume the artificer can move a little on the side to avoid where the firbolg was standing.
Firbolg can do a Dex save to dodge away.
Artificer can roll with disadvantage to hit the forbolg.

Was there a stealth check. or does the artificer knows where the firbolg is?

[Malifice]

Here is the situation, in three consecutive spaces I have an artificer with a thunder cannon, in the next space is an invisible but not hidden firbolg, and in the third space is the bad guy.

Previous turn firbolg used hidden step to go invis, but didn't move. On artificer 's turn they take the now clear line of sight shot at bad guy.

How should I deal with the invisible PC standing right in the path of the shot?

Grant 3\4 cover for the shot. If the PC misses due to cover he hits the Firbolg instead.

[hymer]

I'd treat it the same way I'd treat it if the PC was visible, with two points worth of cover. Mechanically speaking (unless 'thunder cannon' is something mechanical I just don't know about) it's pretty straighforward, and it keeps the game flowing. 5e pretty much doesn't do inadvertent hits on allies, and I see no reason to introduce it.

[Ninja_Prawn]

I'd treat it the same way I'd treat it if the PC was visible, with two points worth of cover. Mechanically speaking (unless 'thunder cannon' is something mechanical I just don't know about) it's pretty straighforward, and it keeps the game flowing. 5e pretty much doesn't do inadvertent hits on allies, and I see no reason to introduce it.

This is what I'd do, too (again, I'm not familiar with the thunder cannon).

[tieren]

Thank you everyone, since the invisible character wasn't hidden I decided to use the partial cover suggestion. I'm not sure yet what I would do in the future if the invisible character were also hidden.

[Ninja_Prawn]

Thank you everyone, since the invisible character wasn't hidden I decided to use the partial cover suggestion. I'm not sure yet what I would do in the future if the invisible character were also hidden.

I say being Hidden does not change the situation, whichever way you rule it. The creature is still there and you don't need to tell the attacker that they're facing an artificially-raised AC.