The Lord of the Rings: Gollum

*MISSABLE*

For these two mutually exclusive achievements, you need to make all decisions in a playthrough as either Gollum or Sméagol. To be clear, the only decisions that matter for these two achievements are the decisions where you need to convince the other personality using argument options. The other options, where you just press either  or ​​​​​​, don't seem to influence this. As a confirmation of which personality you've chosen, Chapter 9 will be titled as whichever is the one you've chosen all playthrough. Note that this will only be the case in the chapter itself. From the Chapter Select screen, it'll always says Gollum, so don't be alarmed. The final decision is in Chapter 10, at the very end of the "boss fight." If you've made consistent decisions throughout, one of these two will unlock.

Note: I believe that it's possible to miss both of these achievements if you switch back and forth between personalities throughout your playthrough. You therefore want to make sure you always win each argument as the same side throughout a run. If you make an incorrect choice during an argument, you can quit out/dashboard and reload to try again and pick the opposite choice.

In terms of unlocking the other of the two, I believe you could theoretically replay chapters to choose the opposite personality. However, it's unclear if you need to do all chapters in order, still play through Chapters 7 and 9 which have no decisions, still play through Chapter 9 where it tells you which personality is in control, etc. It's therefore best to just combine a second playthrough with How Did You Do That? (90G) than risk replaying most chapters only for this achievement to not unlock.