Whenever you attack, put a +1/+1 counter on target attacking creature.
Whenever a modified creature you control deals combat damage to a player, exile the top card of your library. You may play that card this turn. (Equipment, Auras you control, and counters are modifications.)
Araña builds a wide, aggressive RW board where creatures are 'modified' by counters, Equipment, or Auras, then hits face to put counter on an attacker and impulse-draw extra cards off combat damage. You snowball card advantage every combat, deploy threats, suit them up, and swing repeatedly until the table is buried in pressure or you alpha strike for lethal.
Built-in card advantage that grows as your board widens and connects each turn
Cheap 3-mana commander that immediately rewards attacking, keeping curve low and aggressive
Synergizes with the strong modern 'modified matters' package (counters, Equipment, Auras)
Aggressive RW colors with efficient anthems, haste, and combat tricks
Impulse draw is symmetrical with board wipes—lose your creatures and the engine stalls
Hard to use exiled cards if you flood mana or hit lands you can't deploy that turn
Vulnerable to fogs, deathtouch blockers, and pillow-fort decks that punish attacking
No inherent evasion, so big blockers can shut down the combat-damage trigger