It'll definitely see play in commander, standard, and modern formats, as the cheap casting cost and four powerful abilities really make it stand out from the rest
Despite how powerful it is, you won't see many people wielding this card in the wild, since it's banned in almost every game format
With that in mind, expect Tiamat to rise up in price the longer Adventures in the Forgotten Realms is around
I also think these suggestions probably give away the direction I would try to take the deck with my changes: a more efficient, interactive deck that focuses on ramping toward Sauron mana reliably alongside a mix of interaction and reanimated monsters to impact the game in the meantime
This ability lets me fix my mana perfectly, getting anything from a [c]Taiga[/c] to a [c]Godless Shrine[/c] into play
Ancient Tomb Description : Ancient Tomb taps to add 2, with the downside of dealing 2 damage to you