The First Sliver turns your creature curve into an unstoppable cascade chain the more Slivers in your deck, the more reliable the chain becomes
Once you get access to 7 mana, you just get three cards from your library that you can cast for free
If you ever wanted Prince John from Robin Hood to sing A Part Of Your World from Aladdin, this is the game that lets you do it
All I recall is that I won this game
There are enough ways to get it back from your graveyard in this format that it will give you 3-for-1 potential sometimes too This will let you rummage when you attack or crew a vehicle, but perhaps most importantly, it lets you do it when you tap it using one of the many cards in this format that lets you tap artifacts and creatures for value
Though undoubtedly strong, this card is probably a bit too slow to be main-deckable in Modern: three mana for the sword, two more to actually equip it, and then you have to get through to deal combat damage as well