Attribute checks with six-sided dice

I replaced normal (basic/expert style) Attribute checks with this:

Ancient Roman bone dice
http://www.ancientresource.com/

System

Roll D6s under your Attribute score to success.

Difficulty

How many dice, how easy it is to roll under, is determined by the difficulty of the task.

Easy - 2D6
Normal - 3D6
Hard - 4D6
Extreme -5D6

Double Sixes Always Fail

No matter how many dice you roll, two sixes is always an failure.

Wild Die

If the character class should know how to do it, roll an extra die of different color - wild die. Wild die result can be used to replace any other die result.

Teamwork

How many people can help in a task depends on the situation, space around it, individual capability, etc. All additional participants' Attribute modifiers are added together and divided by three. This is extra wild dice that can be used.
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Examples

Example 1: Roger the Thief tries to remember very hard has he heard anything about weird incidents in the city sewers. The town is quite big and Roger is familiar with it, so the task should be easy (2D6). For the fun of it, Charisma score is used. Roger rolls 4 and 6 (10), under his Cha of 12 and has heard rumors considering the sewers...

Example 2: William the Fighter tries to bend bars of the cage his fellow adventurers are locked in. The bars are rusty, so 3D6 are rolled against his Strength. Other characters locked inside will help him, with total Strength bonus of 4, so they add one wild die. William, as a Fighter is supposed to do tour de forces, so he adds another wild die from his class.

Example 3: Time is running out when a friend is suffering severe magical poisoning. Time cannot be wasted but there are just so many books in this arcane library. Magic-User Matthew rolls 4D6 trying to score under his Intelligence. But he knows them books, getting a wild die to help his task.

Example 4: Weird old engine of ancient dwarves. All the pieces seem to be collected, but now it is time to assemble it. The adventurer party of four puts their heads together and start the job. Difficulty is extreme, 5D6, but at least they get three wild dice. Intelligent ladies they are.

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Inspiration:
Praedor roleplaying game by Burger Games, +Ville Vuorela
Liberation of the Demon Slayer by Kort'thalis Publishing, +Venger Satanis