If the creature can't attack any of those players but could otherwise attack, it must attack an opposing planeswalker (controlled by any opponent) or the player that goaded it
If an artifact enters the battlefield under your control and then Sentinel Sarah Lyons enters the battlefield under your control later in that turn, creatures you control will still get +2/+2 that turn as long as Sentinel Sarah Lyons remains on the battlefield and under your control
How you play with/against summons varies immensely on a per game basis
Furthermore, this card is also incredibly frustrating to get rid of for the opponent because it can special summon itself from the GY by banishing a light and dark attribute monster from the hand or the GY
Sometimes, Pokemon card ability text may allow you to do this, but the most common way of skipping an evolution stage is by using a Trainer card such as Rare Candy
6 - First Edition Base Set Holo Charizard Holographic cards are always more desirable