Can Blink and Banishment be combined to have an effect similar to Etherealness?

Question

Imagine the following sequence of events:

1. The wizard casts blink.
2. During the next turn, he uses his Ready action to cast banishment on himself once he is in the Ethereal Plane.
3. The banishment brings him back from the Ethereal into the Material Plane; since the Material Plane is his home plane, he can still maintain concentration on the spell.
4. During his turn, he dismisses blink as an action, then breaks his concentration on banishment as a free action.
5. This results in the wizard being returned to the Ethereal Plane, trapped there until he casts banishment again, and this time holds concentration for the duration of the spell.

Question: is there something wrong with this? Can you point out exactly why this wouldn’t work?

As you guys can see, these steps grant the caster an enhanced version of the spell etherealness, using a 3rd- and 4th-level spell slot, instead of the 7th-level spell slot required for etherealness.

Answer 1

This should work

Let's go through step by step and I'll go through every requirement

Cast blink

As long as he has a 3rd level spell slot, a free hand, and can speak this is no problem for your wizard.

This means at the end of your turn there is a 50% chance that you will be on the Ethereal Plane until your next turn starts.

Readies banishment

To cast banishment and hold the magic (the crux of the Ready action for Cast a Spell), he will need something he distastes which should be fairly easy for your wizard to figure out. The trigger for the Ready action must be perceivable which entering the Ethereal Plane certainly is.

While on the Ethereal Plane, you can see and hear the plane you originated from, which is cast in shades of gray

Let's assume you rolled an 11 or higher on blink (if not you have to wait until next round for this plan to work, and your spell slot is expended). Banishment has a different effect depending on the plane the target is on. Since your wizard is on the Ethereal Plane due to the blink spell (reactions take effect after the trigger), and his native plane is the Material Plane, he will be transported back to the Material Plane until the spell ends as long as he fails the save.

You may be unable to willingly fail a saving throw in 5th edition and if your wizard succeeds, he will have to try again next turn with a new 4th level spell slot.

Cancels blink

All you need for this is an action, which you get on your next turn. Since you are already on the Material Plane, blink does nothing at the start of your turn. (emphasis mine)

At the start of your next turn, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.

Breaking concentration

There is no such thing as a "free action" in 5th edition, but ending concentration takes no effort on your part.

You can end concentration at any time (no action required).

When he ends his concentration (as long as he does so within 1 minute of casting the spell), banishment returns your wizard to the space he cast it from, on the Ethereal Plane.

If the spell ends before 1 minute has passed, the target reappears in the space it left or in the nearest unoccupied space if that space is occupied.

Low-level etherealness?

This isn't quite low-level etherealness since your return method of banishment has an undetermined destination whereas etherealness ends by returning you in the spot you occupy. Banishment places you in an undisclosed location and as such, your GM decides.

Answer 2

Everything works as you've described

However, even though your idea works, it does not mean it works well, or that it is a replacement for Etherealness.

First of all, you expend your spellslot when you ready the spell, not when it triggers and that readied spell is wasted if you don't use it before your next turn. Moreover, you cannot choose to fail your banishment save.

So between blink-less turns and banishment saves, your chances of wasting 4th level spell slots is significant. For example, assuming you are a 7th level wizard with 18 int and 8 cha, on average you'll have to try (1/(.5*.75)) ≈ 2.67 times before succeeding. Each attempt expends your only 4th level spell slot.

The return trip is also a problem. You can use banishment to get back to the Material Plane, but where exactly you'll end up is entirely up to your DM. A 7th level character would be functionally retired for months or years as he/she travels from a random location on the Material Plane to the party's last known location.

By contrast, Etherealness is meant to facilitate travel and exploration. You can just walk (float?) past 8 hours worth of dangers or obstacles and then conveniently reappear at your new location. It's a completely different functionality compared to your idea, which permanently places you in the Ethereal Plane, with no convenient means of return.