For modders: Yes, replacing this file breaks Steam achievements/online, but some mods require a cracked DLL. That's on you. For normal players, keep the legit Steam file and whitelist it.
It sounds like you're looking for a user-style review related to a issue for WWE 2K15 . That file is the Steam DRM wrapper—if it's missing, modified, or flagged by antivirus, the game won't launch. steam api 64 dll wwe 2k15
Here's a review written as if from a frustrated player on a forum or store page: Works fine if you understand the steam_api64.dll dance Rating: ★★★☆☆ (3/5) For modders: Yes, replacing this file breaks Steam