The level mechanic is pleasantly different from actual level monsters for two reasons, one that is better and one worse, keeping it in good balance overall
Squirrel Girl gets straight to the point on producing squirrels, and the absence of a on the activated ability is well nuts
her standard art variant is much cheaper, of course, at around $3
Though the Marvel Secret Lair release was horribly bungled, the fact that fans have been able to share their bonus cards so quickly does illustrate the one big advantage of the new Secret Lair model (from the perspective of players that is)
Its very reminscent of Krenko, but the advantage here is that all of those Rats are likely unblockable, which makes them very dangerous
This enter the battlefield effect would normally cost you two mana on its own, so the fact that it's tacked onto Siege Rhino provides incredible value