Evaluating items in Dota is much tougher, compared to comparing hero stats. With heroes, we can look at their win rates in different brackets, at their popularity, and at least get a general idea of how they fit into the current meta and why. With items, the situation is much harder, but today we will try to use somewhat limited tools at our disposal to figure out whether Mage Slayer is underrated.
The items we see on this page and their corresponding stats are what players have in their inventory at the end of the game. This is important, as it decreases the win rates of “tempo” items that are purchased in the midgame to gain an advantage, but are later sold.
The effect was most apparent a couple of years ago when Drum of Endurance was a must-have item on any team and pubs followed suit, but it still had a sub-50% win rate, as successful players simply sold them by the end of the game, to free up an item slot.
As such, relying on these statistics blindly is hard. What we can do, however, is compare 
Mage Slayer as the end-game item to similarly priced end game items.
This month, Mage Slayer had a ~56% win rate as a slot in the inventory in the late game. It has a cost of 3250 gold and as such can be considered to be in the same price category as a wide variety of items. We counted twenty one such item, starting with some of the cheapest complex artifacts such as 
Witch Blade, 
Maelstrom and 
Eul’s Scepter of Divinity and ending with 
Kaya, 
Sange and 
Yasha derivatives, as well as 
Battle Fury.
Of these, only eight items have a higher win rate as an end game inventory item:
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850 gold more expensive and slightly overtuned Sange, Kaya, and Yasha derivatives all get over 58% win rate. Sange and Yasha, the most likely to compete for a slot with Mage Slayer, is at 58% exactly, so the cost-benefit is comparable. Moreover, in some games having both can be worth it.
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Specific teamfight-enhancing items, such as
Pipe of Insight and 
Crimson Guard are at ~58% win rate. These are teamfight items and when used correctly in a correct game they can have a massive effect. Pipe alone is potentially 2000 extra HP for your team. -
Lotus Orb is still one of the best defensive options with an almost 60% win rate in the end game. It is that good in the later stages of the game. It is also usually built by supports, so if a support has almost 4000 gold to spare, chances are – their team is winning. -
Aeon Disk together with 
Solar Crest are the only two items that outperform Mage Slayer, while costing less gold. The former is unsurprisingly OP with a 59.5% win rate, while the latter is ahead of Mage Slayer by 0.10% this month.
Stats-wise, Mage Slayer is seemingly decent. It outperforms having a Battlefury in the late game and is even ahead of 
Diffusal Blade. It is also better than 
Desolator, 
Heaven’s Halberd and 
Orchid Malevolence.
Naturally, it is only at its best in very specific games and low popularity indeed often results in a higher win rate, since the item is built only when players know what they are doing and why they need it, as opposed to building default. Yet, it is still proof enough that there are games where Mage Slayer is good and worth considering. We just need to figure out how to identify these games.
With a name like Mage Slayer one would assume the item is at its best when dealing with mages. Nukers and high burst damage heroes like 
Zeus, 
Queen of Pain, 
Invoker, 
Skywrath Mage etc. are who come to mind when one hears the term “Mage”. While the item is certainly decent against them, we don’t think it is at its best against them.
The problem with Mage Slayer and Mage interaction is that any competent player who knows how to play a nuker type of hero will try not to be in the range of an auto-attack before unloading their arsenal of magics. They want to appear on your radar for a brief window, cast their spells on a priority target very fast and disappear into the shadows, before your team gets to react.
Mage Slayer won’t do anything against them, even if you manage to catch them afterward: the damage is already done and the Mage Slayer debuff at this point is close to worthless.
It doesn’t mean the item is useless, however. Far from it, in fact, especially in the current patch, where we witness a resurgence of heroes like 
Leshrac, 
Bristleback, 
Necrophos, 
Timbersaw and such. Heroes who deal high sustained damage, but need to be at the front of the fight, are usually the ones who will suffer from Mage Slayer the most.
Sure, the magic resistance on Mage Slayer might not be very effective against Bristle or Timber, who are physical and pure damage heroes, but the debuff itself is already worth it. When Bristleback’s Quill Spray starts dealing 350 physical damage instead of 550, or when Timbersaw’s nukes all start dealing less than 150 pure damage, it is pure value, no pun intended.
Against someone like Leshrac, it gets even prettier: under the debuff, even with the level 20 talent, Leshrac deals 155 damage from each pulse, before reductions. A hero with Mage Slayer will be taking roughly 85 damage per second after all reductions, which is quite manageable. More importantly, they will be helping their team and their supports survive.
We think the item was misnamed, resulting in it being underappreciated. “Frontline Hero With High Sustained Damage-Dealing Capabilities Mitigator” is a bit of a mouthful, sure, but it would be a much more accurate description and would probably result in it being more popular and perhaps even more successful.
What do you think of the item now? Did we convince you to at least give Mage Slayer a shot, or do you still think the item needs a couple of buffs? Leave your thoughts in the comment section below.