Battering Ram

The second meaning is, "finalize an item on the chain." This is the play that appears in other conditional statements and effects that check if cards have been played, in cards like Battering Ram, Crescent Guardian, and the Legion dependent keyword.

I have a Ravenbloom Student on the board and I haven't played any spells this turn. What happens when I play Rebuttal targeting my opponent's Stupefy and pay [A] on resolution? After everything resolves, how much will Battering Ram cost? Will my opponent's Legion abilities be active?

Ravenbloom Student will trigger twice, Battering Ram will cost [4], and your opponent's Legion abilities will be active.

Ravenbloom Student's triggered ability checks whether a spell that you control resolves. You gained control of the Stupefy, and it resolved, so you will have triggered Ravenbloom Student's ability. Battering Ram and Legion, on the other hand, check whether cards were finalized. Although you gained control of Stupefy, you did not finalize it; you got it after it was already finalized by your opponent. Thus, your opponent's Legion abilities will be active, and Battering Ram will only receive a [1] Energy discount.

Relevant Rules: 419.4., 419.4.a., 419.4.b.

419.4.b. Non-triggered abilities that check cards being played do so by means of referencing whether said cards have been Finalized. Example: A player plays a spell, which is countered by Defy. Any Legion abilities of game objects controlled by that same player will be active. Example: A player plays a spell, which is countered by Defy. If that player plays Battering Ram and has played no other cards that turn, it will cost [4] Energy.