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?