We Want...A SHRUBBERY is something you can play in any of your Commander decks running green, since it can fetch out dual lands and triomes since you can put any Forest on the battlefield, not just a basic
This might seem like a low range but in practice Sunlance kills way more things
Not only is this an immensely powerful activated ability, but the fact that Ulamogs Dreadsire has vigilance means you can stay on the attack while also building up your board
Its fine to kill something like Gaelicat with it, but I havent felt especially bad about not starting one
The most likely reasons are if it's sacrificed, if it's legendary and another legendary permanent with the same name is controlled by the same player, if it's a planeswalker and another planeswalker with the same subtype is controlled by the same player, if it's a creature with toughness 0 or less, or if it's an Aura that's either unattached or attached to something illegal