Slivers you control and nontoken creatures you control are the chosen type in addition to their other creature types. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.
, : Create a 1/1 colorless Sliver creature token.
Choose one creature type as Rukarumel enters and your entire nontoken army (plus your Slivers, creature spells, and cards in hand/library/graveyard) becomes that type, letting you stack tribal lords, anthems, and 'choose a creature type' payoffs onto creatures that would never normally share a tribe. You spend the early game ramping and fixing across five colors, deploy Rukarumel, and snowball into a wide board buffed by typal effects while her activated ability drips out 1/1 Slivers as fuel. You close games by overrunning the table with anthemed creatures or by assembling a Sliver/tribal engine.
Five-color identity gives access to the best ramp, removal, card draw, and tutors in the format
Turns disparate goodstuff creatures into a unified tribe, so every Sliver lord or typal anthem buffs your whole board
Affects cards in hand, library, and graveyard, supercharging 'creature type matters' tutors and payoffs
Built-in token engine creates a stream of Slivers without needing the rest of your board
Most of the deck's power is locked behind Rukarumel resolving and sticking, so she's a removal magnet
Choosing a type is locked in on entry, making the choice awkward against information you don't yet have
Five-color mana bases are expensive and prone to stumbling without strong fixing
Largely creature-dependent, so board wipes set you back hard
Lets you tap two same-typed creatures to cheat out more creatures, trivially online since everything matches.
Tighten the mana base with the best dual lands, fetches, and fixing rocks (Chromatic Lantern, Arcane Signet, Birds of Paradise) so five colors comes online reliably. Add fast mana and protection for Rukarumel (Swiftfoot Boots, Heroic Intervention, counterspells) and lean into a focused payoff package—either a critical mass of Sliver lords or universal anthems plus a tutor suite. For higher power, build toward a compact combo line such as Sliver-based infinite mana or Cryptic Gateway chains rather than relying purely on attacking.
Legendary Creature — Human Wizard
, 
: Create a 1/1 colorless Sliver creature token.