4. Hidden God Of War/Kratos Boss Battle - Shovel Knight
For 2015's next-gen release of the phenomenally charming Shovel Knight, developer Yacht Club decided to include two very specific easter eggs; the Xbox One version getting a Battletoads boss fight that riffed on the infuriating Speederbike level - and the PS4 having Kratos himself show up. However, rather than make the showdown easy to find, you instead need to find a specific item to trigger it. Firstly, accrue 5000 gold coins to purchase a pass into the Hall of Champions, then head up and across to the top right of the set of rooms, bouncing on the tile that's as far right as possible - there you'll find a map with the iconic Omega symbol. Heading outside will make a random enemy appear nearby on the map, whereupon beating him gets you some flame-chained shovels and different-coloured armour, just for kicks.