Tip on unlocking those last couple characters

[Nat the Chicken]

The last two characters, in the bottom row next to the custom characters, will probably be the final things you get in the game. The Blacksmith unlocks automatically once you've crafted the last Mithril item (for which you need all 250 Mithril Bricks and all 18 designs). Lurtz (Newborn) unlocks "once you hit 100%." I was just having trouble getting him to unlock after I got the Blacksmith, but then I figured it out, so I thought I would explain the problem I had.
I crafted the last item, the game saved, and _then_ the Blacksmith unlocked. I got the achievement for all characters at that point, but no Lurtz Newborn, and my pause screen said 99.8%. I wandered around outside for a while wondering how to unlock him. Then finally I figured out that the game doesn't autosave when the Blacksmith unlocks, and it doesn't update the percentage until progress gets saved.
Normally to force a save I'd go find a Mithril Brick or something to unlock (this is my typical approach to saving in Lego games, especially older ones often don't have a way to manually save), but there isn't anything left at that point. So the only way to save the Blacksmith being unlocked is either to quit to the title and choose the save option (which I didn't realize existed lol), or to enter a level and then immediately save and exit. I quit to the title, then noticed that the file said 100%, and when I loaded it I had Lurtz (Newborn). A little unsatisfying, so if you want the dramatic unlock animation you can do the level trick.

Also, I'm going to use this as a PSA to NOT USE THE SAVE STATUES IN THIS GAME!!! If you unlock collectibles in a level, use a save statue, and then your game crashes or you quit out and you finish the level later, it can miscount the items and often cheat you out of a Mithril Brick reward. This is permanent, locks your file out of 100%, and can't be fixed in any way I know for sure. It's happened to me too many times, don't let it be you.

[Nico]

There's a final cinematic in the starting area on 100%, though the game's compass does a poor job bringing you there, that should probably trigger a save after the credits