At what character levels should this homebrew maul be upgraded?

Question

One of my player (playing a level 3 warforged barbarian) came to me with a request to be given a multi-staged legendary maul. I came up with the following item, but I'm still wondering at which character level I should provide each stage.

Meteor (stage 1)
Maul, uncommon (requires attunement)

You gain a +1 bonus to attack and damage rolls made with this magic maul.

Meteor (stage 2)
Maul, rare (requires attunement)

You gain a +1 bonus to attack and damage rolls made with this magic maul.

You can use a bonus action to speak this magic maul's command word, causing its head to glow a faint light, not enough to improve any lighting. The glowing lasts until you use a bonus action to speak the command word again or until you drop or sheathe the maul.

While the maul is glowing, it deals an additional 1d6 force damage to any target it hits as part of an attack.

Meteor (stage 3)
Maul, very rare (requires attunement)

You gain a +2 bonus to attack and damage rolls made with this magic maul.

You can use a bonus action to speak this magic maul's command word, causing its head to glow a faint light, not enough to improve any lighting. The glowing lasts until you use a bonus action to speak the command word again or until you drop or sheathe the maul.

While the maul is glowing, it deals an additional 2d6 force damage to any target it hits as part of an attack.

Meteor (stage 4)
Maul, legendary (requires attunement)

You gain a +3 bonus to attack and damage rolls made with this magic maul.

You can use a bonus action to speak this magic maul's command word, causing its head to glow a faint light, not enough to improve any lighting. The glowing lasts until you use a bonus action to speak the command word again or until you drop or sheathe the maul.

While the maul is glowing, it deals an additional 2d6 force damage to any target it hits.

While the maul is glowing, you may use your action to hit the ground with the maul. Each hostile creature in 30-foot radius circle centered on you must make a Dexterity saving throw (DC 8 + proficiency bonus + STR). Each target takes 8d6 force damage and falls prone on a failed save, or half as much and not falling prone on a successful one. Once you used this ability, you may not use it until you finish a short rest.

I emphasized changes between the stages to make it clearer what changes between phases.

I'd like to give the stage 1 now (level 3), but at which character levels are stages 2, 3 and 4 best upgraded so I can wrap my story around it?

Answer 1

RAW

The Dungeon Master's Guide on page 135 has a table of suggestions for Magic Item Rarity and when players may expect to get such items:

Rarity	Character Level
Common	1st or higher
Uncommon	1st or higher
Rare	5th or higher
Very Rare	11th or higher
Legendary	17th or higher

Using this table, stage 2 would be around level 5, stage 3 at around level 11, and stage 4 at around level 17.

Non-RAW

It depends on your game. How long do you plan on playing this campaign? Is this a level 1-20? If so, the above RAW answer might be best, maybe with a bit of tweaking (level 17 seems high to me).

If you plan on playing to a different level, you would have to change the levels with something that makes sense. If you're playing until level 12, maybe power it up once every two to three levels.

Alternatively, if you have a set story progression in mind, it may be better to have it power up at specific checkpoints in the story - each quarter or so. That way you don't need to worry about them leveling up with side quests and awarding it before you have planned.

And as always, do what is most fun for the group. If the barbarian seems to be falling behind the rest of the party in regards to power, maybe push the power up ahead a bit.