The following are known Action Replay Codes for Batman Beyond: Return of the Joker on Nintendo 64 (N64).

Device Compatibility: Action Replay & GameShark

Enable Code
f11942c02400

Infinite Health
802086f20064

Infinite Lives
802086f00009

Infinite Batarangs
802086fe000f

Press L For Super Key
d01bb02d0020
812085242000

Press Z For One Hit Boss Kills
d01bb02c0020
801fc5970000