You can beat him with Vanar but it isn’t easy.
Let’s get the obvious stuff out of the way. As always, play around Makantor and Lavaslasher. So for example if you wanna put a Rex down, make sure you can move far away from it so they can’t Makantor you next turn. Or if they put metallurgist down first turn, play your stuff outside of Lavaslasher range.
Lavaslasher is only really scary when it gets to proc fight on turn two which can very clearly be played around, most other times it’s just a worse Brightmoss Golem and it shows if you play around it. You will feel the tempo loss as the game goes on.
If they play stuff that dies to rebuke, you play stuff that dies to rebuke.
If they play stuff that dies to plasma storm, you play stuff that dies to plasma storm. If you look at the deck I posted for example, if they have a bunch of metallurgist golems, and I have to choose between wisp or mentor, I’ll go with mentor. if they have a bunch of 4/4 lavaslashers and I have the choice between Kron and Letigress, I’ll go with Kron.
One really really good card is Sworn Avenger and it’s a devastating turn one play as the second player. If it survives early on, it becomes immune to natural selection and forces them to eventually waste Lavaslasher or Makantor on it mid game. In general Lavaslasher and Makantor HATE being spent on targets with high attack and Sworn Avenger is one of them.
You can also set up plays with Frostburn the same way they do with their board clears, because after all they have to be the aggressor. So if they have a bunch of little minions, move back and put value generators on board to encourage them to move forward giving you a big Frostburn.
If you’re getting to the lategame and you haven’t won yet, you gotta start preparing for finality and look for Lightbender. In general if I draw a Bender, I’m very conservative with it and I will only use it if I have to. You might not draw more than one throughout the course of the game and you will need it to counter finality.
Sometimes the Vaath player might be meming with Kraigon instead of Finality which is the proper way to play, so it pays well to also have Hailstone Prison and EMP in hand when at that stage.
Corner provokes with Kron are relatively easy to pull off in this match up because most of the time, Vaath doesn’t have many minions on the board around him. So for example if there’s a Lava Slasher 2 spaces in front of him, walk forward and put Kron in the bottom left corner and body block the slasher with your general and cover the other space adjacent to Kron and Vaath and your general with a cheap minion. Rex is perfect for the job for example because it doesn’t die to Vaath even if he has buffed his attack. If you are forcing him to punch the Kron with his face you’re getting value.
That’s all I got.
Here’s an example game that illustrates everything I talked about:
Played recently while I was rank 1