What are the different endings available in Batman: Arkham Asylum
Solution 1:
The endings are completely randomized. You've seen 2 out of the 3 endings. The other hand that you may end up seeing is that of:
the Scarecrow.
Neither playing the game through on different difficulties nor acquisition of Riddles will affect what ending you receive. And far as players have been able to determine, it's either completely random, or it's based on variables obfuscated enough that the playerbase can't figure it out.
Solution 2:
They are 3 different endings and they are random. So nothing to do... it just happens in a random way.