as long as the cost are not similar, the source is a valid target.
{s}{s(creature|mybattlefield)}
or
{t}{t(creature)}
or when the card states specifically that the source is not valid such as
"{t},sacrifice another creature you control:draw a card"
as long as the cost are not similar, the source is a valid target.
{s}{s(creature|mybattlefield)}
or
{t}{t(creature)}
or when the card states specifically that the source is not valid such as
"{t},sacrifice another creature you control:draw a card"