Fri rörlighet (PHB, p244):

You touch a willing creature. For the duration, the target’s movement is unaffected by difficult terrain, and spells and other magical effects can neither reduce the target’s speed nor cause the target to be paralyzed or restrained.

The target can also spend 5 feet of movement to automatically escape from nonmagical restraints, such as manacles or a creature that has it grappled. Finally, being underwater imposes no penalties on the target's movement or attacks.

En grell Tentacles attack (MM, s172):

Hit: 7 (1d10 + 2) piercing damage, and the target must succeed on a DC 11 Constitution saving throw or be poisoned for 1 minute. The poisoned target is paralyzed, and it can repeat the saving throw at the end of each of its turns, ending the effect on a success.

The target is also grappled (escape DC 15). If the target is Medium or smaller, it is also re strained until this grapple ends. While grappling the target, the grell has advantage on attack rolls against it and can't use this attack against other targets. When the grell moves, any Medium or smaller target it is grappling moves with it.

Så om du misslyckas med att konstitutionen räddar under fri rörlighet, blir du fortfarande förlamad av giftet?