ShroudShroud is a static ability. “Shroud” means “This permanent or player can’t be the target of spells or abilities.”
Multiple instances of shroud on the same permanent or player are redundant. (CR 702.18) (This enchantment can't be the target of spells or abilities.)
: Put X tower
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on this enchantment.
At the beginning of your upkeep, if there are 100 or more tower
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on this enchantment, you win the game.