A 1999 Super Robot Wars game released for Nintendo 64, and the only game released for the console. It was the first SRW game to feature animations in a pseudo-3D space. The game can use the N64's Transfer Pak add-on to unlock extra bonus units by connecting to SRW Link Battler, a Game Boy Color game.
The game's original characters and mecha are notably absent from the Original Generation games, likely due to copyright issues arising from it being codeveloped by Monegi, Inc. This would also explain why the original units in Advance have such similar designs as the ones in 64 - to the point that 64's original mecha are mentioned as their predecessors in the OG timeline, despite never actually showing up in the games.
This tag implicates super_robot_wars (learn more).