Are goblins immune to opportunity attacks?

Question

Last night at my table, my party faced a goblin village. We pretty well know the goblin stat block contains the Nimble Escape trait. But still our DM never ever showed us that any goblin disengaged and since we had no visual clue, we thought the goblin were opportunity-attackable. Yet we could never land any opportunity attack on the goblin horde despite several uses of Dissonant Whispers (mostly on goblin bosses since they're the only ones with a bit of HP).

So can the DM use goblins' disengage bonus actions without clue and make all the goblins virtually immune to opportunity attacks, or should it be made obvious to players that goblins use their disengage bonus actions?

Answer 1

Goblins can avoid opportunity attacks on their turn, but Dissonant Whispers should help.

Disengage states:

If you take the Disengage action, your movement doesn't provoke opportunity attacks for the rest of the turn.

If goblins use their bonus action to Disengage every turn, you cannot even attempt to hit them (as there is no trigger to use your reaction).

But! Notice "for the rest of the turn" clause. In DnD5 combat consists of rounds, and rounds consists of turns. In a round each creature gets a turn, according to initiative order. As soon as creature finishes and another creature starts its actions, it means that one turn ended and another one started. Any effects which works "until the end of current turn" or "for the rest of the turn" stops working now.

When goblin finishes his turn and your bard starts his, goblin loses benefits of Disengage. When you cast Dissonant Whispers goblin moves using his reaction:

On a failed save, it takes 3d6 psychic damage and must immediately use its reaction, if available, to move as far as its speed allows away from you.

The fact that he uses his reaction makes following passage on forced movement and opportunity attack avoidance non-applicable:

You also don't provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction.