How to improve odds of using Amulet of the Planes?

[RickAllison]

The Amulet of the Planes is an awesome tool, allowing unlimited uses of the Plane Shift spell so long as you can succeed on an Intelligence check of DC 15. The problem is that it is only an Int check rather than a skill check, which makes it harder to reliably reach that DC. I would like to get this item as reliable as possible under certain conditions:

1) 22 Int (+6)
2) +6 character proficiency bonus
3) You can use either a rare and two uncommon magic items or up to six uncommon magic items
4) Anything from any core books, adventures, Unearthed Arcana, or Planeshift materials is approved
5) As few levels as possible.
6) The Help action is not an option for advantage. It is assumed that the Int check is such that another person cannot assist.

My current plan would use the ibis-headed aven from Planeshift Amonkhet (Jack of All Trades for only Int checks), grab Guidance from Magic Initiate or something similar, and pick up a Luckstone. That doesn't require any levels in classes, but gives a minimum roll of 12

[LeonBH]

With a +6 Proficiency bonus, you're already at least level 17.

Then take 2 levels of Bard for Jack of All Trades (+3 to checks made without your proficiency bonus). This brings you to a +9.

Cast the level 2 spell Enhance Ability, and enhance your intelligence. Now you have advantage on the roll. This is a concentration spell so you cannot cast Guidance on yourself anymore.

You can now hit a DC 15 with a probability of 93.75%.

To further stack the deck, if you have another Bard in the party, ask them to give you Inspiration (1d6). If you have a Cleric, ask them to give you Guidance. Pick up the Lucky feat somewhere so that you can take the best of 3d20, instead of 2d20. If you start Variant Human, you can have this feat at level 1.

Now your probability is 99.98%.

If you need magic items to support an Amulet of the Planes, use the Luckstone, which grants +1 to ability checks and saves.

Your minimum roll is now 13 if you roll a 1 on all of the dice, and your chances are 99.99% that you will pull it off.

If you didn't have a Bard or Cleric to assist you, that's fine. Your chances are still 99.20% without the Guidance or the Inspiration.

You could also be a Halfling instead of a V Human. You can re-roll a 1 on your 3d20, which I shall not go into the trouble of calculating, but it should bring your chances up even higher.

[mephnick]

I love items that are basically a TPK in disguise.

[TheTeaMustFlow]

I love items that are basically a TPK in disguise.

Eh, we had one in my last game - they're not very dangerous, since you can just press the button again next round. Assuming you're a decently high level once you get them, there's not much the planes can do to you in that time. The only real problem is Carceri if you're running its optional rule, but that's one plane in 19.

[LeonBH]

I love items that are basically a TPK in disguise.

You mean, an I Win button in disguise?

[RickAllison]

You mean, an I Win button in disguise?

Intentionally failing the check with good movement could be an excellent way to clear out a few tough enemies. You know, providing you don't die from the plane. Or from being the only target for these ticked-off enemies. This seems like a bad idea, now that I think about it...

[Kuulvheysoon]

There’s a new common magic item from Xanathar’s (not a category specifically allowed, but it’s less rare) called the Clockwork Amulet (or something to that effect) that allows you to treat a d20 roll as a 10 once per day. That’d guarantee at least one success, more if you are allowed to grab more.