Characters enter the field in the ready position - meaning they are orientated upright - but cannot be used or exerted until the following turn
Now, because of the current (how do I put this...) "unsteadiness" of Standard for the next few days, you might not feel comfortable committing to a Standard deck in the same way
Its worth noting that one of the downsides of running Slime Against Humanity as your singleton-buster instead of, say, Hare Apparent, is that youre not actually casting a creature spell each time
My personal favorite battle, Invasion of Ikoria, offers a flexible ability on the front that scales at different points of the game, and then sets up an outright win on the back with a giant creature that features a unique ability of its own to push through massive damage against your opponent
Powerful permanent combat trick