I was reading the Devourer stat block from Volo's Guide to Monsters and noticed that one of his actions (Imprison soul) states:
...the devourer regains 25 hit points, immediately recharges Soul Rend, and gains an additional action on its next turn. VGtM page 138
That made me wonder if a devourer can use Multiattack twice on his next turn.
I can't find anything in the Multiattack rules that prevent this, but it feels weird.
This is, in effect, no different from the Fighter's Action Surge class feature:
On your turn, you can take one additional action on top of your regular action and a possible bonus action.
Since the Attack action uses an action, he can effectively use Action Surge to Attack action twice in one turn.
In addition, the Extra Attack class feature grants multiple attacks per Attack action, which behaves similarly to the Multiattack action that some creatures have.
We know that Multiattack is an action a monster can take. If a monster has two actions, then it stands to reason it can Multiattack twice if it has two actions, in the same way that the Fighter can Attack action twice with Extra Attacks when using Action Surge.
