Activated mana abilities may be played both when a player has priority and in process of casting a spell, activating an ability, resolving a spell or ability, if any such action requires a mana payment
But Im often surprised by the lack of card knowledge shown by a lot of other people
A 3/2 flyer that effectively couldn't be blocked was pretty much a bomb, since there were few removal spells, fewer fliers, and virtually no tempo in this format
The latter is rarer than the former but you don't need this to win the game for you for it to be good either
The last new mechanic is actually more a new spin on something Un-sets have been doing since their inception - reaching beyond the table to affect the people and things around the players
That means with instant spells, you can trigger the effect on your opponent's turn and copy all the spells already exiled with Arcane Bombardment