Are these Homebrew "Blackfrost Gauntlets" too strong for a monk?

Question

I have a group of level 15 (soon level 16) characters. One of them is an Ascendant Dragon Monk. I have homebrewed an item for my group and am certain that the monk is the only one who would use it. This is the item in question:

Blackfrost Gauntlets

very rare (require attunement)

The gloves have 5 charges for the following properties. They regain 1d4+1 expended charges daily at dawn.

Infuse Weapon

You can use your bonus action to infuse a simple or martial (melee) weapon with the biting cold of the Blackfrost for 1 minute. Black and blue ice begins to cover the weapon. Weapon attacks made with this weapon count as magical for overcoming resistances. If the gloves have at least one charge, the infused weapon deals an extra 1d10 cold damage to any target it hits.

Biting Cold

When you hit a creature with the infused weapon, you can expend 2 of its charges to force that creature to make a DC 16 Constitution Saving throw. On a failed save, the creature is restrained by ice. The ice remains until the start of your next turn or until the creature takes bludgeoning or fire damage. If it takes bludgeoning damage in this way, that damage is increased by 2d8.

Frigid Wrath

When you roll cold damage, you can expend 2 of the glove’s charges to deal maximum damage, instead of rolling. If the cold damage is from the infused weapon, it costs 1 charge to use this property instead.

Ice Lance

You can expend 1 charge of the gloves to summon a dark ice shard in your hand. You can make a ranged attack with it, using a +10 attack bonus against a single target within 120 ft. On a hit the target takes 3d8 cold damage. You can spend more than one charge at a time. The damage increases by an additional d8 per extra charge used.

I might take the melee restriction away from the "Infuse Weapon" property but this is not the part I might have an issue with. I feel like in theory the monk might be able to infuse his fists with the Blackfrost but I am uncertain if I should allow this. I worry that this is too strong regarding the potential "free" damage upgrade he would obtain with this. At level 15 he deals on average 3d8 + 15 dmg without spending a Ki point on Flurry of Blows (not including his +2 Insignia of Claws he carries). Which is on par with an Eldritch Blast for a Level 15 Warlock, who is also part of the group. The additional d10 on each attack would pretty much double the damage output of this PC. The other party members are a sorcerer, bard and warlock (for potential reference regarding damage since they are spellcasters).

I am looking for feedback regarding how I could handle this situation. My instinct was to say that the Blackfrost can only be infused into weapons because a mortal body cannot handle it and the blood would freeze. Another option would be to somehow limit the amount of times the additional d10 triggers per turn, but that feels somehow like cheapening the item. Or am I completely overthinking this and the damage upgrade would be fine?

Answer 1

This is fine for a very rare weapon, just a bit complicated

Firstly, by level 15, the game has left the level range where encounters based on the DMG encounter guidance are actually balanced. At these levels, monsters that follow guidance tend to deal too little damage, and have a hard time to really challenge players. Our DM for our level 15 group often overloads the encounter budget for a "deadly" encounter by multiples, and that is after ignoring to apply XP modifiers for multiple monsters at the same time. And these fights still are survivable. That means, the players really do not need any aditional help from strong magic items at those levels. But on the other hand, as balance is already out of the window anyways, even if you hand out a strong item on top of it, it does not matter that much. But this item is not overpowered, as we shall now explore.

How good are the blackfrost gauntlets in comparison to other very rare weapons, with an eye towards a monk? Because you limit uses per day, this will depend on the number of encounters you run per day. If you keep the players on some sort of ticking clock as you should to keep them from five-minute-workdays (i.e. something bad is going to happen soon, so they cannot afford to rest too often and early and have gap days), then on average the item will recharge to have 3.5 uses per day.

The average number of encountes per day in practical play is about 3, more if you run weaker ones. The average encounter lasts for about 3 rounds, more if the fighting is dragging out, or these are larger fights. That means, in a typical day you can expect 9 rounds of combat or more.

The benchmark for very rare magic weapons in regards to damage is the oathbow with an added 18.6 expected extra damage per attack over a baseline bow. You can use that every round throughout the day, so it will deal a total expected extra damage of about 335 points if you assume the wielder has extra attack -- more if they are a fighter, or have some way to generate bonus attacks (less if opponents are immune or resistant to poison, which at those levels many are, so it is not quite as good as it looks at first glance). Even the merely rare flametongue deals and extra 7.3 expected damage, or about 130 points per day.

With your weapon, as a baseline, the infused weapon always deals 5.8 extra damage per attack (including criticals). As you have 3-4 uses, you can use it as a bonus action every fight (conserving the last charge so it deals the extra damage), and use it every round, but then you have nothing left for the other special features. That still is less than the merely rare flametonge, adding up to about 104 extra damage. This may be a bit nicer for the monk, as they can infuse their monk weapon, and use their bonus action for another attack on top of extra attack, bringing it to about 150 extra damage (the bonus action first round is spent on activation), a bit better than a flametongue, but still short of the bow.

Using an infused monk weapon adds about 5.8 x 3 x 3 damage in such a three-round bash, or 52 damage in total. That is your baseline to benchmark the other abilities against.

Using it is far better than spending a charge to just deal an expeced 4.5 damage more one single time from frigid wrath, or burning one to deal an expected 14 damage (with crits) using the ice lance for that charge (they should have around +10 to hit from Ability score bonus and Proficiency Bonus by level 15, so no difference there). The only other application that might be worth it is Biting Cold, because the restrained condition is nasty, and even for a single turn can save a lot of damage for the characters due to imposing disadvantage on the monster, and dish out a lot of extra damage, if all other party members attack with adavantage, which averages out to +4 or +5 to hit. But all of that is pretty situational. (And Con DC 16 is not that hard a save at high levels - average at CR 15 is +10, so it will work only 25% of the time, a bit more if you guess good targets).

So overall this is weaker than some other very rare weapons you could hand out, but still worthwhile -- after all we have been comparing against the very best options. If anything, it is a bit bloated and burdened with abilities most of which will rarely be used if the players think it through. You could just allow these gauntlets to imbue a weapon with darkfrost, and it would play very similar.

PS. You may want to consider limiting this to non-magical weapons. Otherwise, you can add this on top of something like the oathbow or a flametongue for the fighter. And I would recommend to limit it to your own weapons -- the ability does not do that as written. Otherwise you can just give it to a henchman or minion, and have them attune and imbue your or the fighter's weapon, making both the bonus action cost and the attunement cost effectively moot.