Players who are looking to evolve their Magmar into a Magmortar will need to get a Magmarizer in Pokémon Legends: Arceus, though how the item can be used has changed from past games. The Magmarizer was introduced in Pokémon Diamond and Pokémon Pearl alongside Magmortar and was traditionally an item to be held by Magmar so that it could evolve when traded. Since Pokémon can no longer hold items, the Magmarizer has been changed to work similarly to an evolution stone such as the Dawn Stone in Pokémon Legends: Arceus.
The Magmarizer is the sister item to the Electirizer, which evolves Electabuzz into Electivire. However, unlike the Electric-types, a Magmarizer will evolve Magmar into Magmortar to further build upon the Pokémon's strengths in its Special Attack stat. Furthermore, Magmortar receives increased defense stats and can be a difficult Pokémon to defeat using anything other than a Super-Effective move. As a pure Fire-type Pokémon, Magmortar has twice as many resistances as it does weaknesses, making it an excellent addition to add to any team.
Related: Pokémon Legends: Arceus — How To Find (& Catch) Cyndaquil
Similar to both Magmar and Magmortar themselves, players can easily find a Magmarizer by collecting the items inside the Space-Time Distortion areas of Pokémon Legends: Arceus. The biggest obstacle is that, like all other evolutionary items in Pokémon Legends: Arceus, the Magmarizer has a rare chance of spawning due to the large number of items it has to compete against. Fortunately, if players do manage to find one Magmarizer in a Space-Time Distortion then, usually, they can find one or two more before the zone disappears. While there isn't a way to spawn Space-Time Distortion areas more frequently, players
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