Here is the full list of all 25 Rikki & Vikki achievements.
Pick up or catch 100 boxes during a playthrough.
Smash a Scarab.
Listen to Dut's introduction.
Skip the Intro Sequence.
Complete Single Player Mode without any of Dut's services.
Complete Two Player Mode without any of Dut's services.
Get to Dut's Discount Warps.
Warp back to the Rock Cavern from Dut's Discount Warps.
Refuse Dut's offer to enroll in Direct Dutposit.
Refuse Misery's offer to refight all his guardians.
Warp to the Irregular Cavern.
Complete the Irregular Cavern in Single Player Mode.
Complete the Irregular Cavern in Two Player Mode.
Max out the Irregular Cavern's timer (99:59:59).
Bang Rikki or Vikki's head on the ceiling 256 times in one playthrough.
Complete Two Player Mode without enrolling in Direct Dutposit and only one player purchasing Credits from Dut.
Complete the Single Player Guardian Refights.
Complete the Two Player Guardian Refights.
Enroll in Direct Dutposit from Level R0.
Watch the entire Intro Sequence without skipping any text.
Hit a Fiddler with a box while it's vulnerable.
Get a Fiddler to dunk a box on top of a solid tile, forcing it to break.
Smash a Picky.
Lure a DumBun or BigBun onto a box bridge, then get them to fall.
Use the Warp Bubbles 100 times during a playthrough.