Cavern of Souls

This land enters tapped. T: Add W or U. 3WU: Until end of turn, this land becomes a 4/4 white and blue Elemental creature with flying and vigilance. It's still a land.

This artifact doesn't untap during your untap step. At the beginning of your upkeep, you may pay 4. If you do, untap this artifact. At the beginning of your draw step, if this artifact is tapped, it deals 1 damage to you. T: Add CCC.

+1: Each player discards a card. −2: Target player sacrifices a creature. −6: Separate all permanents target player controls into two piles. That player sacrifices all permanents in the pile of their choice.

+4: Target player exiles a card from their hand. −3: Exile target permanent. −14: Restart the game, leaving in exile all non-Aura permanent cards exiled with Karn. Then put those cards onto the battlefield under your control.

Return up to three target land cards from your graveyard to your hand. Dredge 3 (If you would draw a card, you may mill three cards instead. If you do, return this card from your graveyard to your hand.)

T: Add CC. This land deals 2 damage to you.

Search your library for a card, put that card into your hand, then shuffle.

Return target legendary creature card from your graveyard to the battlefield. That creature gains haste. Exile it at the beginning of the next end step. Splice onto Arcane 2B (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)