A term that was official used when the game was created that has been somewhat phased out is ‘summoning sickness.’ This term does appear in the comprehensive rules, but it is pointed out that this is informal. It refers to the inability of creatures to attack, or use their own activated abilities that have the tap symbol or untap symbol in the cost unless that permanent has been under the control of their current controller since the beginning of the most recent turn. This also applies to permanents that are changed into creatures. ‘Animated’ permanents cannot attack or use activated abilities unless the permanent has been controlled by its current controller since the beginning of this players most recent turn. It does not matter when the permanent became a creature. Creatures with Haste ignore this rule and can either attack or use their activated abilities with the tap and untap symbols.

It is important to note that this does not mean that a creature that has just entered the battlefield cannot be tapped to pay a cost, the only restriction is that it cannot be tapped to pay the cost as denoted by the tap symbol. For example, an Llanowar Elves that has just entered play cannot be tapped to pay the activation cost of its own mana ability. But it can be tapped to pay the activation cost the activated ability of a Heritage Druid even if it is ‘summoning sick.’ In fact, the Heritage Druid itself can be tapped to pay part of the cost of this ability because Heritage Druid’s ability does not contain the tap symbol.