Rules:
• Infinite Mana- You are considered to have infinite mana of all colors and types (including snow) at all times
• One Spell Per Turn- The core conceit of Type 4, each player can only cast one spell per turn.
• Handling Infinity- If two spells or abilities are infinitely used to top or stop one another, the defender wins.
• All players draw from the same library
• Players start with 5 cards in their hand and have a max hand size of 5 cards.

Check out @Kirblinx and @BoomDooger 's type 4 stacks if you enjoy this format. They've given me a ton of inspiration and have much more detailed writeups on the format than I've provided here.