Shanna, Sisay's Legacy can't be the target of abilities your opponents control.
Shanna gets +1/+1 for each creature you control.
4/27/2018 Spells your opponents control can target Shanna.
4/27/2018 Shanna’s ability that modifies its power and toughness applies only while it’s on the battlefield. In all other zones, it’s a 0/0 creature card.
4/27/2018 As long as it’s on the battlefield, Shanna’s last ability will count itself, so it’ll be at least 1/1.
4/27/2018 Because damage remains marked on a creature until it’s removed as the turn ends, nonlethal damage dealt to Shanna may become lethal if other creatures you control leave the battlefield during that turn.