Phyrexian Dreadnought Phyrexian Dreadnought, the infamous old classic, is a 1-mana 12/12 with trample
Sliver Support There are a handful of cards that directly support Slivers, and then there are a bunch of cards that can support decks that have a heavily focused tribal theme: Hive Stirrings, Hivestone, Sliversmith, Cavern of Souls, Cover of Darkness, Kondas Banner, Packs Disdain, Shared Triumph, Standardize, Steeling Resolve, Unnatural Selection, Adaptive Automaton, Alpha Status, Descendants Path, Faces of the Past, Harsh Mercy, Luminescent Rain, Shared Animosity, Urzas Incubator, Call to the Kindred, Distant Melody, Door of Destinies, Mana Echoes, Riptide Replicator, Roar of the Crowd, Belbes Portal, Coat of Arms, Cryptic Gateway, Patriarchs Bidding, Vigean Intuition Changelings Lets also not forget that Lorwyns changelings are Slivers too
Untap her, do it again, cast a Triskelion of infinite size
Whatever you use, I'd strongly encourage you track this closely, especially when playing in competitive Limited Aetherdrift events where these are bound to see play
Note that she triggers when you have a creature arrive to the battlefield, not cast