In other words, that's four mana of value you can gain the same turn she enters the battlefield
Lin Sivvi, Defiant Hero (Ext, S, Block) You might have expected Lin Sivvi to finish higher on the list since she's the one who got banned in Block Constructed, but she's a little slower than the Rebel who finished ninth
In the case of Silver Shroud Costume, this card simply gives a creature Shroud until the end of the turn
In my experience it is often inevitable that a Heliod deck will be able to put one of their combos together, and it might be better to hold instant removal back to break up whatever version they end up finding, lest you waste it early on a redundant or superfluous creature
My general ratio is: lands and ramp, usually a 3713 split 50 mana
Quarum Trench Gnomes from Legends is the first gnome in Magic, but all others were artifact creatures up until Adventures in the Forgotten Realms added some non-artifact gnomes