VigilanceVigilance is a static ability that modifies the rules for the declare attackers step.
Attacking doesn’t cause creatures with vigilance to tap. (See rule 508, “Declare Attackers Step.”)
Multiple instances of vigilance on the same creature are redundant. (CR 702.20)
When Gandalf enters,
exileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) up to three target lands you control, then return them to the battlefield tapped under their owner's control.
LandfallAn ability word has no rules meaning of its own. It groups abilities with similar themes; the text following it explains this card’s effect. (CR 207.2c) — Whenever a land you control enters, draw a card and put a +1/+1
counterTo 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 Gandalf.