Immediate Abilities (IMM) are a new type of Ability created by Zanbaku. An Immediate Ability, unlike an ACT Ability, can be used at any time, an example of an Immediate ability would be;
[IMM](VC):[Counter Blast (2)] This unit gets [Power]+4000 until end of turn.
While this ability, used on your turn, would frankly be terrible, on your opponent's turn, it could be used to gain More-Than-Crossride defense for a turn. This could also be used for abilities with Awkward timing, by adding the timing at the begging of the effect, but after the cost, like so;
[IMM](VC):[Counter Blast (2)] During your opponent's turn, you may pay the cost. If you do, this unit gets [Power]+4000 until end of turn.
This way, abilities are much more flexible, and freedom is allowed with cards. Abilities like this, however, should possibly be costlier if an alternative to an ACT, as CB1 to get +2000 Power on either player's turn is a little strong.