I would assume it'll be like previous events - basically you'll see greater spawn percentages of all fire/ice types, with the common species being literally everywhere and the super-rare species being...a bit less rare, but not common. So probably Slugma, Cyndaquil, Growlithe, and Ponyta will be everywhere for fire types with Charmander and Houndour still being fairly common.
For me the most appealing part of this event would be if they use the opportunity to put Delibird (ice-type) into the game.
