If, during your declare attackers step, Ursine Monstrosity is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under your control continuously since your turn began (and doesn't have haste), then it doesn't attack
Decks are twenty cards as opposed to sixty, and Energy is auto-generated each turn, though youll have to specify what kind(s) you want when youre building the deck, and if you choose more than one, the type of energy youll get is random
Until then, may you know the joy of watching your own children grow and change.
As it turns out, he was way off, by more than $15,000
Many seem attracted to the dream of curving Woodweavers Puzzleknot into spiking an Ulamog, the Ceaseless Hunger on turn 4, but I just dont see building your deck in that manner as a realistic path