Global Skills

Global skills (not to be confused with skills) can be bought with green shards, but only when you are not in a challenge or endless mode. Each new global skill purchased additively increases the price of all global skills by 10%, and each upgrade increases the prices by a further additive 1%. Here is a list of them with all manner of useful information:

Detonator
The Detonator is a global skill which is only used in endless mode. Depening on the skill level you get a bonus to your collected green shards if exploded in the given time window.