Jenova Cells — Whenever Sephiroth attacks, you may put a cell counter on target creature. Until end of turn, each modified creature you control has base power and toughness 7/5. (Equipment, Auras you control, and counters are modifications.)
The Reunion — , Sacrifice a modified creature: Return this card from your graveyard to the battlefield tapped.
Sephiroth is a midrange aggro Boros commander built around the 'modified' keyword: load up creatures with counters, Equipment, and Auras, then attack and use Jenova Cells to push a creature to 7/5 (or larger if it already exceeds that) while turning your whole board into 7/5 beaters for the turn. You assemble a wide, modified board, swing for huge damage, and use The Reunion to keep recurring Sephiroth from the yard for repeated alpha strikes.
Commander grants a board-wide power anthem on every attack, enabling explosive turns out of nowhere
Built-in recursion (The Reunion) makes him resilient to removal and lets you turn a dying modified creature into a fresh threat
Counters from any source (cell counters, +1/+1 counters, charge counters) all count as modifications, so synergies are extremely broad
Boros has deep Equipment, Auras, and go-wide token support to keep creatures 'modified'
The 7/5 buff is a base P/T set, so it can actually shrink your already-large creatures
Needs creatures to be modified to benefit, so a board wipe or artifact/enchantment removal can blank the ability
Red/white lacks card draw and ramp, so you can run out of gas in longer games
Color identity limits access to black's tutors and recursion despite the aristocrats-flavored Reunion ability
Relies on combat damage, making it weak against fogs, mass blockers, and lifegain pillowfort decks
Legendary Creature — Human Avatar Soldier
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