Legends of Runeterra has many card effects that are common enough that they get their own keyword - a word or two that immediately tells you how the card works. Let's take a look at the Rally keyword.
If you don't have one, gain the attack token. You can attack this round.
Dictate the terms of war and battle when you feel like it, regardless of whether or not you have the Attack Token. Such is the power of Rally.
Rally gives you an Attack Token as long as you do not already have one, allowing your units to go on the offensive when before they could not. This could mean you gain the Attack Token on your opponent's round, or, better yet, after you've already used your regular attack, so you can strike twice!
Keywords that Work Great with Rally
Quick Attack or Double Attack work especially well with Rally, allowing you to get the jump on your opponent's units multiple times. By attacking before the blocker has a chance to respond, you can wipe out several units over the course of the game, all with just one Rally-unit.
Playing Against Rally in Legends of Runeterra
There is no strategy that specifically targets Rally at this time in the game's life, although most Rally cards are Champions/units. The best way to deal with Rally is to kill the Champion it's attached to, preferably with a removal spell so-as-to ensure the problem stays dead.
Example Legends of Runeterra Rally Cards
Katarina is an annoying Champion to catch! After she strikes, both in Level 1 and Level 2 form, she Recalls back to your hand to hide. With Quick Attack as well, your opponent will need some other way of defeating her besides simple combat.
Lucian's Level 2 form Rallies every time an ally dies, which can be often in combat. His Double Attack means he'll almost always survive the combat, allowing for multiple Rally opportunities.
Relentless Pursuit is pretty straightforward, allowing you to Rally at any given moment. Use this to double-up on attacks for the round, or to surprise your opponent with an attack on their turn!
Tianna Crownguard is an example of Rally on a non-Champion unit, leading her forces into battle. Her heavy stats and Tough keyword will keep her on the table for a long time.