Berlin is drawish.... main line has an interesting Marshall attack. The bird variation and the jaenisch gambit are two others. Good luck for your tournament Tommy!
Best variation against the Ruy Lopez??
the Ruy is sound, there isn't a variation that "gives an advantage" for Black so just play a main-line that you know very well and hope for the best

When I used to play 1...e5, I like the "Steiner var." a lot:
https://www.chess.com/openings/Ruy-Lopez-Opening-Marshall-Attack-Steiner-Variation
comp say it's bad, but if White makes One mistake... oh dear.
[he would Know the main line of the Marshall Attack, oh horse. my guess is, he would play anti-marshall once you 0-0, like, he would play a4].
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GM Seirawan suggests a draw-me-or-lose technique:
Hold a Draw Against a Higher-Rated Opponent - GM Yasser Seirawan - 2013.06.06
https://www.youtube.com/watch?v=qejc9ISNMBU
he give a 'ruy lopez' example, and really go deep into it.
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I know one thing about a Ruy - The Breyer is an improvement to the Chigorin. yes, horse back to the stable. very stable var.
https://www.youtube.com/watch?v=9Aev-Asmq6k
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One thing I saw Magnus doing, is, instead of that manouver of playing Be7, 0-0, Re8, and then fianchettoing the e7 bishop, he just play g7 and fiachetto at once. - gaining time. how come people didn't think of it before, is beyond me.
Hey Tommy, In this variation what does your opponent play after castles? The main moves are c3, a4 and h3. If c3 you could play d5 and study up on the Marshall attack. If a4 Bb7 is pretty good and if h3 you are kinda forced to play d6 and go back to the main line.

Hey Everyone!
I have a game in a tournament coming up, and it's against a player who plays the Ruy Lopez.
Is there a variation that black can play to fight for the advantage, because I don't want to go main line or Berlin endgame
I always play e4 e5, so please don't tell me to just play another opening!!
Many thanks!
Give 3...f5 a try

Steinitz thought 3...d6 is the strongest. You can also play 3...Nf6 and 4...d6 like Capablanca did.
Steinitz was over 200 years ago and that theory is mostly outdated
4... d6>4...Nxe4 but eh

The Neo-Moeller is strong, and quite rare- only some patzers like Magnus Carlsen are employing it regularly. There is also a new, quite good book on it.
However, you cannot learn all the stuff in a few days, and in any case, it is 101% sure that the opening evaluation will be quite irrelevant to the game result.

Hey Everyone!
I have a game in a tournament coming up, and it's against a player who plays the Ruy Lopez.
Is there a variation that black can play to fight for the advantage, because I don't want to go main line or Berlin endgame
I always play e4 e5, so please don't tell me to just play another opening!!
Many thanks!
Give 3...f5 a try
I love the Schliemann defense! Naroditsky drew with it against Dominguez Perez yesterday in the US Championship. Give it a try. However, if your opponent is Dominguez, don't expect to draw.......
I know, I watched the game
Hey Everyone!
I have a game in a tournament coming up, and it's against a player who plays the Ruy Lopez.
Is there a variation that black can play to fight for the advantage, because I don't want to go main line or Berlin endgame
I always play e4 e5, so please don't tell me to just play another opening!!
Many thanks!