Laboratory is a game about a scientist fighting creatures that got out of control and destroying his lab.
Each creature is a boss battle designed to challenge your instinct and reflexes, and if you will succeed and manage to defeat one of them - you will be rewarded with a valuable upgrade to your character that will help you later on with your next fight.
And if you will (somehow) manage to overcome all 3 of the creatures - there will be a big bad one waiting for you to try and defeat it.
No in between levels - Overcome challenges - Win and get your new upgrades.
