Z Assists are preset attacks you can call in your assist characters to perform. All Z Assists are meterless special moves that are a part of a character’s special move list, such as Gohan’s (Adult) “Jet Upper”, Tien’s “Dodon Ray”, and Goku’s (Super Saiyan) “Kamehameha” just to name a few. Most Z Assists are usually beams, projectiles, explosions, or strikes of some sort, but there are some unique exceptions such as Krillin’s “Senzu Bean” and Android 18’s “Barrier”.
You can perform a Z Assist if it is available by pressing A1 or A2. You can also have 2 Z Assists active at the same time. Z Assists are unavailable when they are on cooldown from just being used, and are also unavailable during other interactions such as blocking or getting hit, the assist character being dead, and during Super Attacks, since hitting A1 or A2 during a Super Attack will perform an Ultimate Z Change. Another aspect of Z Assists worth noting is that they can’t be performed while dashing on the ground, since 6A1 and 6A2 will give you a Z Change. Be careful when approaching the opponent and trying to call a Z Assist and be sure to briefly return to Neutral sometime in the process of approaching if you want to call a Z Assist.
Do not fret though, for Z Assists are insanely useful attacks purely due to the fact that they can be called independently while your active character performs other actions. Z Assists do not interrupt whatever action your Active Character is performing. Therefore, Z Assists very much so become supplemental actions that can make for overwhelming pressure and extended combos. You can even use them to combo off of the 6M overhead, giving you a scarier overhead option for your opponent to deal with.
Be cautious of how Z Assists are called though, for Assist characters are open to being attacked upon entering the stage and until they leave stage. In addition, your character will not perform their Z Assist attack immediately. There are a couple of frames after your Z Assist is called and before they perform their Special Attack where they will be vulnerable. You’ll want to make sure that there is no reason why your Z Assist will be struck for the duration they are part of the battle (with the exception of Android 18’s Z Assist of course). If a Z Assist is hit, they can be put into a damaging combo, however all damage they incur will be counted as blue health. If your active character and Z Assist character are both hit (Trust me, it happens), they will both be put into a dangerous combo where they both take damage. Not only that, but the attacker will gain double the meter for their combo than they normally would since they are hitting two characters. A combo simultaneously performed on two characters is frequently called a “Happy Birthday”. Don’t ask why it’s called a “Happy Birthday”. It’s a term that comes from the games in the Marvel vs Capcom series, but as far as the origination goes, it is beyond me. The following question must of course be “What is it called if all 3 of your characters get hit? A ‘Merry Christmas’?”. Personally, I’d just call that a mistake.