What happens after a creature of the chosen type penetrates my Magic Circle?

Question

The Magic Circle spell description says:

• The creature can't willingly enter the cylinder by nonmagical means. If the creature tries to use teleportation or interplanar travel to do so, it must first succeed on a Charisma saving throw.
• The creature has disadvantage on attack rolls against targets within the cylinder.
• Targets within the cylinder can't be charmed, frightened, or possessed by the creature.

What happens after a creature of the chosen type penetrates my Magic Circle? Does a character lose the other protections of the Circle for that creature?

I had always assumed no. I thought the creature could then try to knock or drag them out of the circle, but those attempts would still be made at disadvantage. And as long as they remained in the cylinder the character would still be immune to the creature's charm, frighten or possession attempts.

An answer to a question about an inverted Magic Circle made me doubt my understanding. It made it sound that it is the barrier (the surface of the cylinder) that provides those defenses not just the state of being inside the field defined by the cylinder. I think my confusion lies in that the rules text doesn't say something like, "As long as the creature is outside the circle it has disadvantage..." or "...can't be charmed, frightened, or possessed by the creature as long as it is outside the circle." The only criteria I see is that the targets have to be in the cylinder, nothing about where the creature is.

Answer 1

The description of Magic Circle reads (in part):

You create a 10-foot-radius, 20-foot-tall cylinder of magical energy centered on a point on the ground that you can see within range.

• The creature can't willingly enter the cylinder by nonmagical means.

• The creature has disadvantage on attack rolls against targets within the cylinder.

• Targets within the cylinder can't be charmed, frightened, or possessed by the creature.

A creature of the specified type may not enter the volume demarcated by the spell (unless they use a spell). A creature may direct attacks into the area (at disadvantage) because the target of the attack is within the cylinder. These attacks would have to be ranged attacks or attacks with a weapon long enough to reach the target without their appendage crossing the edge of the cylinder.

Additionally, the creature may not grapple or shove or make any kind of unarmed strike against a creature within the circle because doing so would require a part of their body to enter the warded space.

So long as a target is within the volume of the cylinder, the creature's attempts to charm, frighten, or possess the target automatically fail regardless of where the creature is positioned. It's the target's location that is relevant for that part.

However

If a member of the specified creature type is forced into the zone unwillingly (bypassing the "can't willingly" prohibition), they may then drag the target out of the space to remove the handicap of attacking with disadvantage (or continue to attack with disadvantage from inside). They would need to drag the target out of the area of effect in order to charm, frighten, or mind control the target.

The grapple check to accomplish this would be made normally (ie not with disadvantage) since it uses a contested roll, not an attack roll.