Would a Lich/Wizard casting Globe of Invulnerability, Prismatic Wall, and Shield (as needed) be "invincible"?

Question

In Dnd 5e, would casting Globe of Invulnerability at 8th level (concentration) on a surprise round, then Prismatic Wall (action) around the caster at the top of the next round, and Shield (Reaction) as needed to deflect projectiles, cause a caster to be essentially unkillable for the duration, barring other high-level magic, or exceptionally high ranged attack rolls? This strategy seems to prevent all conventional sources of damage, but is there some caveat I haven't thought of? Can you teleport into a Globe of Invulnerability, and then somehow avoid the damage of the Prismatic Wall?

Is there a way to additionally have them cast a ritual spell, or read a concentration spell scroll while concentrating on Globe of Invulnerability? Could followers cast spells on them while inside the sphere?

Answer 1

Probably not, a simple dimension door might do it

You can simply teleport there with dimension door through Globe of Invulnerability, which does not block it.

Wether Prismatic Wall would stop you is unresolved, there are highly upvoted answers for both sides. It is not an obstacle that you cannot see inside, as you do not need to see the target space with dimension door, but the question is if you can select a spot in there as the target area. My take is that the argument this does not work as you cannot target a spot is flawed: you also cannot target any other spot you do not have a line of effect to, and it is generally understood that you still can dimension door onto the other side of walls or doors. So my take is, you get in. If you do, you are not passing through the wall, so you take none of the ill effects from the various layers.

The spell is only 4th level, and allows you to take along a barbarian or other smasher with high Con. This is useful as you both still have to save against being blinded when you arrive due to being close to the wall, and you want to avoid being blinded because it imposes disadvantage to attacks.

With high to hit bonus the smasher can attack and hit the caster, and even a shield will not make them safe from that. If as a barbarian he attacks recklessly, the advantage essentially will offset shield. Once they are hit, they have to make a concentration check for their globe, too.

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For your side questions (which you probably should remove, as they are really unrelated to the main question):

There is no way to concentrate on more than one concentration spell, but there is a workaround in putting such spells into a glyph of warding if they are legal for being put in there: then, for example for spells that conjure creatures, the glyph will take care of the concentration.

Globe of Invulnerability does not care about allied or friendly or hostile creatures, it cares about where the caster is when casting the spell:

Any spell of 5th level or lower cast from outside the barrier can't affect creatures or objects within it, even if the spell is cast using a higher level spell slot

Once you are inside the barrier, you can cast at the creator of the globe without a problem.

Answer 2

Dispel Magic exists. Globe of Invuln only blocks magical effects that target something inside it, not effects that target the Globe itself.

Misty Step is also a very easy way to get past the Prismatic Wall. Since you cast Misty Step on yourself, and not on the point you're moving to, whether the wall provides cover or not is irrelevant. They would have to make the save to avoid being blinded once they get to the other side, though.

Alternate possibilities:

Druid can Wildshape, or a player can be Polymorphed, into something with Burrow, and go under the wall.

A player could use a non magical source of fire, or acid, etc, to cause a ground effect and force the enemy to start making Con saves. So just a molotov cocktail basically.