Myr Battlesphere

Mana cost: {7}
Type: Artifact Creature — Myr Construct
Power / toughness: 4 / 7
Set: The Brothers' War Commander #151 (rare)
Price: $0.38 USD

When this creature enters, create four 1/1 colorless Myr artifact creature tokens.
Whenever this creature attacks, you may tap X untapped Myr you control. If you do, this creature gets +X/+0 until end of turn and deals X damage to the player or planeswalker it's attacking.

Myr Battlesphere has 16 printings, first in Scars of Mirrodin (2010). EDHREC ranks it #932 among Commander cards. It appears most in Urtet, Remnant of Memnarch decks (16,984 on EDHREC). 12 public decks on TCG run it. It has 3 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: not legal
standard: not legal
brawl: legal

Public decks that run Myr Battlesphere

Built from Scratch - Commander 2014, led by Daretti, Scrap Savant
Built from Scratch - Commander Anthology Volume II, led by Daretti, Scrap Savant
Creative Energy - Modern Horizons 3 Commander, led by Satya, Aetherflux Genius
Eternal Bargain - Commander 2013, led by Oloro, Ageless Ascetic
Exquisite Invention - Commander 2018, led by Saheeli, the Gifted
Growing Threat - March of the Machine Commander, led by Brimaz, Blight of Oreskos
Invent Superiority - Commander 2016, led by Breya, Etherium Shaper
Keen Engineering - Foundations Commander, led by Sai, Master Thopterist
Lorehold Legacies - Commander 2021, led by Osgir, the Reconstructor
Mardu Surge - Tarkir: Dragonstorm Commander, led by Zurgo Stormrender
Rebellion Rising - Phyrexia: All Will Be One Commander, led by Neyali, Suns' Vanguard
Urza's Iron Alliance - The Brothers' War Commander, led by Urza, Chief Artificer

Commanders that run Myr Battlesphere most

Deck counts from EDHREC.

Urtet, Remnant of Memnarch: 16,984 decks
Dr. Eggman: 10,342 decks
Breya, Etherium Shaper: 6,460 decks
Urza, Chief Artificer: 6,263 decks
Brudiclad, Telchor Engineer: 3,393 decks
Tannuk, Steadfast Second: 3,253 decks
The Capitoline Triad: 3,151 decks
Osgir, the Reconstructor: 3,051 decks

Often played with Myr Battlesphere

Cards that show up in the same decks on EDHREC.

Rulings

2020-08-07: You choose the value for X as the last ability resolves. You can't choose a value for X that's greater than the number of untapped Myr you control.
2020-08-07: As the last ability resolves, you can tap untapped Myr you control even if Myr Battlesphere is no longer on the battlefield by then. If that has happened, Myr Battlesphere won't be able to get the +X/+0 bonus, but it will still deal X damage to the appropriate player or planeswalker.
2020-08-07: You can tap any untapped Myr you control as the last ability resolves, not just the Myr tokens you created with the first ability. This includes Myr that haven't been under your control since your most recent turn began.