Oath of the Gatewatch: mechanics

Oath of the Gatewach set is on the way, hence it is high time to introduce new mechanics:

• Surge - you may cast this spell for its surge cost if you or a teammate has cast another spell this turn. The first spell may be countered or be still on stack, but you are anyway entitled to use surge ability. It usually brings mana savings, but some cards have additional effects too.
• Support N -  put a +1/+1 counter on each of up to N target creatures. If a creature has an ability support, you cannot target the creature itself. You cannot target one creature twice. 
• Cohort - an activated ability of Ally creature requiring tapping it and another Ally you control in order to do something.