Hey, high legend wild gamer here
What beats Raza?
Faster combo decks. Remember that at its core, Reno priest is still a control deck that has a combo slotted in. Of course they do have their combo disruption, but other than that the combo decks appreciate the generally passive nature of the deck and the lower amount of draw the deck has. Some good examples of these are Mozaki mage, Malygos druid and Darkglare warlock.
What if you want to play a control deck? I hear LPG mage is supposed to be okay into it. However I cannot confirm this statement, as I do not play the deck myself and I know very little about the deck. Warlock is not that good into the deck, but there are cards that improve the matchup, namely Tickatus.
How can you tech against Raza?
Grizzled Wizard and a card that changes hero powers can be used in combination to change Shadowreaper Anduin's hero power. Sir Finley is typically paired with it, but I've seen Galakrond, the Tempest be used instead in a Galakrond shaman I saw on ladder once. However, if the opponent hasn't played Zephrys, do note that they can use it to generate a Jaraxxus as an out for after you change their hero power.
If Dirty Rat pulls Raza and they are not able to retrieve it with cards such as raise dead and seance, they will likely lose the game. However, that's a very difficult thing to do. Pulling a Spawn of Shadows or Pen Flinger will alleviate a lot more pressure. You can also try to lock out the Raza priest for a few turns by chaining together Loathebs and use these turns to set up a 2 or 3 turn lethal, but this doesn't happen often, and I think that you should wait until you see your opponent play some specific cards before you commit to this.
There's also Bad Luck Albatross and Tickatus and probably some other disruption card that I can't think of right now that people like, but I don't think that they're that worthwhile inclusions unless the majority of your games are against decks where these aren't deadweight.
How do you actually play against Raza priest?
Put them on their back foot. Pressure their health as much as you can so that you can prevent the spawn from coming down, and count spawn lethals, both on yourself and your opponent. If you can get them to play their strong AoEs and removals and pressure them more immediately afterwards you're in good shape. Run them out of cards in hand so that they don't have enough resources to ping you down. Remember, they have a finite amount of strong removals. One of the plays they can make is to play their cards, then use Mindrender Illucia to leave you with a hand full of useless cards so keep this play in mind.
Obviously this is easier said than done, but priest beats up on many board-based strategies. This includes against decks such as the Archwitch Willow builds of Renolock and a lot of aggro decks.