TERRARIUM - Anthophobia Dev blog

Hello Watch, You can unlock pixel animation gallery once you defeat the boss monsters in game.
Once you defeat boss 1/2/3 at chapter 1/2/3, V1.00 gallery will be unlocked, then once you defeat the boss monster of chapter 1.5/2.5/3.5, V1.50 gallery will be unlocked, then once you defeat boss of chapter 4 and 5, the final version of H replay gallery will be unlocked

if that is too much, you can always use cheat code to defeat the bosses easily.
also this game encourages you to use cheat code by awarding player an achievement.