Zenkai Units-
Oh, boy. It's already time to explain Zenkai, huh? And how they keep picking units I just do not have... (ノ´ー`)ノ
Originating in November of 2019, Zenkai Awakening was the Bandai Namco and Dimps' way of making older units stronger without pumping out balance changes. Accompanying Zenkai Awakening was the shift to Red Stars, meaning that units could now hit 14 Stars instead of just 7. This had... an interesting effect on the community that I will not be speaking of here, because to this day it is still controversial. Instead, I will just be explaining what it does.
The process is fairly simple, but it does take a bit of work. Additionally, they changed the process in July 2020 in order to streamline the newer Zenkai units, so I will be explaining how to obtain the older ones and the newer ones. However, the base requirement is the same: you must have the unit that can be Zenkai Awakened (or Zenkai'd) at 7 Stars or 3,000 Z Power at the minimum. Otherwise, your copy of the Zenkai unit will not be eligible for the process until it has a higher Z Power level. This was previously remedied by the Master's Pack Z banner, which guarantees a Sparking unit for each multi, and each Sparking unit is eligible for Zenkai Awakening through the old method with the current exception of RED Super Saiyan Trunks (Teen) (DBL02-02S). Yes, it includes Beerus.
However, while the method of obtaining them changed, what the Zenkai Awakening does has remained the same. Zenkai Awakening grants each unit a strong buff in base stats when they first reach Zenkai Level 1, or Z1, as well as a new set of 60 Soul Boost Panels. Z1 also unlocks their first set of Zenkai Abilities, which are locked to a color and a tag that the Zenkai unit shares, such as RED + Saiyans, and buff all four main stats, Strike Attack and Defense and Blast Attack and Defense. This is not the case for the F2P Zenkai units, but I'll be covering those in a bit. In total, there are seven Zenkai levels, meaning it maxes at Z7. At Z3, the unit unlocks their second Zenkai Ability, which raises the percentages that they buff the units that match their color and tag, their first Zenkai Passive, and their special card sleeves. The Zenkai Passives differ from unit to unit, but they must be unlocked by maxing out the Zenkai unit's Soul Boost panels for that specific Zenkai Level, which in this case would be the "Adept" Soul Boost Panel. Z4 is when the next Zenkai Ability is unlocked, Z6 for the second passive which follows the same requirements as the first except with the "Powerful" Soul Boost Panel, and Z7 is when the last Zenkai Ability is unlocked.
For the old Zenkai units, of whom will be listed shortly, there are a set of Zenkai Awakening Missions that you can complete in order to earn Z1 for free. Notably, it involves increasing their Friendship Rank to 10, so using them in your daily Let's Fight! requirements is recommended. The other requirements are just beating the stuffing out of units from a certain tag, so it's not complicated at all, just time consuming. Each banner has received its overhaul into the new form of Zenkai banners, so you will no longer go broke summoning for the older Zenkai units.
Old Zenkai Units:
RED Super Saiyan Goku (DBL01-04S)
BLU Legendary Super Saiyan Broly (DBL01-35S)
GRN God of Destruction Beerus (DBL07-11S)
GRN Majin Buu: Good (DBL06-06S)
PUR Super Saiyan 2 Gohan (Youth) (DBL04-11S)
YEL Goku Black (DBL06-13S)
BLU Final Form Cooler (DBL08-10S)
For the Zenkai units released after the new process, there will be no missions to get them to Z1 for free, instead they have a Zenkai banner that nigh guarantees 1 Zenkai level or higher per 1,000 CC, as it incorporated multi summons with a very large increase in the Awakening Z Power it gives. In total, this makes it more accessible to players who do not spend on the game, although they have to make the decision to either spend on the Zenkai banner for one unit or a new banner, such as a Step-Up in order to get multiple units. It's a personal decision, which I will not be discussing here. Instead, have this list of New Zenkai Units.
For any Legends Limited Zenkai Units, their Awakening Z Power will be added to the Ultra Space Time Medal Shop for 2k Awakening Z Power each USTR reset. You can purchase the Awakening Z Power even if your copy of the unit is not 7 Stars, and when they do reach 7 Stars, they'll have the Zenkai Level of the Awakening Z Power you have purchased.
New Zenkai Units:
RED Super Saiyan Trunks (Teen) (DBL02-02S)
GRN Android #16 (DBL05-06S)
PUR Vegeta (DBL01-17S)
YEL Demon King Piccolo (DBL05-08S)
RED Perfect Cell (DBL4-04S)
RED Super Saiyan 2 Gohan (Youth) (DBL10-06S) - (Legends Limited)
YEL Android #18 (DBL03-06S)
BLU Super Saiyan Bardock (DBL07-04S)
BLU Goku (DBL15-05S) - (Legends Limited)
PUR Super Saiyan 3 Goku (DBL06-11S)
GRN Legendary Super Saiyan Broly (DBL12-01S)
BLU Super Saiyan God SS Goku (DBL13-01S)
RED Super Gogeta (DBL05-10S)
You might think I forgot, which is a valid concern considering my track record, but no, I did not forget to explain the F2P Zenkai Units. These units are Legends Road units that have come back with a remastered event that allows for the unit in question to be fully limit broken to 14 Stars via a combination of the Shop and the stage in the center of the event, instead of the 6 Stars you were previously locked to with only the shop to use. Once these units are limit broken to at least 7 Stars, you will be able to grind Co-Op until your eyes bleed to obtain 300 summoning tickets to roll on the Zenkai Awakening Z Power banner for free. Each day, you will be given 300 tickets for completing the Advanced Level 3 times, along with the usual reward of Co-Op Medals. Additionally, there are missions that give tickets based on how many Co-Ops you have successfully completed, although unless you have the luck of the gods, you will still need to grind for a while in order to max out the unit to Z7. Currently, there are only 3 units that have this distinction, although it is theorized that eventually all of the Legends Road characters will receive one. Additionally, it is worth noting that Goku (Youth)'s Legends Road returned after Trunks', meaning that if you do not have the resources to finish (this is totally understandable, because my god I had no skips and tickets after this grind), the event will return within the year. Most likely, that is.
F2P Zenkai Units:
YEL Goku (Youth) (DBL-EVT-01S)
BLU Trunks (Youth) (DBL-EVT-03S)
GRN Gotenks (DBL-EVT-04S)
Recently, there have been a series of overhauls for the oldest story events in the game, namely "Raditz Attacks!" and "Nappa the Cruel!". Not only do these events now have the modern map-based interface along with giving more CC, they also feature their specific EX Unit as a F2P Zenkai. Given the small amount of time between Raditz's and Nappa's overhaul releases, it can be reasonably inferred that there will be multiple sets of EX Zenkai units based on those permanent story events, and possibly the rotating ones as well. The major difference between the two Zenkai types, besides rarity, is that EX Zenkai units only buff units that are of their element and are EX units, such as BLU + EX or RED + EX. Additionally, they only buff two stats instead of the usual four, and only up to 30%, not 40%.
EX Zenkai Units:
BLU EX Raditz (DBL01-21E)
RED EX Nappa (DBL01-19E)
YEL EX Vegeta (DBL03-04E)
BLU EX 1st Form Frieza (DBL01-40E)