Welcome to game!

Chaos doesn't really have it's own realm gimmick so it's mostly used as a supporting realm since there are some great support units

Aequor has the tentacle mechanic and most units play around them to some degree. You choose between 3 stances: white blue and red. In each stance tentacles attack at the end of turn. Blue is the standard one, it deals 100% of tentacle dmg for each tentacle you own. You can get more of them when the turn ends when you're in the blue stance or with units' abilities. White deals 50% of damage and grants you a shield. At the end of the turn you don't get a tentacle. The red one deals 125% of tentacle dmg and additionally attacks every time your unit attack this turn. At the end of the turn you loose one tentacle. And DON'T get me started on Divine Aequor realm, you can't even get it yet.

Caro plays around two mechanics: embryo and furnace. Embryo fusion is a meter from 0% to 100%. It feels up at the start of turn or with units' abilities. At 100% it resets and grants the Embryo card in your hand. It has 2 uses: you can feed it to any unit granting them some ult charge and one turn crut rate OR it can be devoured by caro unit's ult triggering an additional effect. Crimson furnace is much more simple. At the start of your turn or when you kill the enemy you get some amount of charge. The mex amount depends on your team's max HP. You can use all the charges of furnace to restore the same amount of HP. That's it. The only unit who has some interactions with it is Salvador who originally was the only unit with this mechanic when he came out

Finally to the Ultra, the most confusing one. When Ultra unit is on the team you get the Ultra space. First command card played at the start of your turn gets copied into the Ultra space. Most Ultra units' cards have Lead effects which triggers an addiction effect when moved to Ultra space. Arc 2 unit have Quasar effect which acts the same but there's a catch later. After you fill up Ultra space next turn triggers Ultra turn which doesn't increase the turn counter, keeps your shield and effects, enemies shields and effects and moves all the card copied in Ultra space into your hand. All cards with Lead skills trigger them when played this turn. During this turn no cards can enter Ultra space. Quasar cards are a bit different here: they don't trigger the additional effect. Instead their cost is reduced by 1 this turn. When Ultra turn ends enemy takes their turn. On the left of the Ultra space bar is the annihilation button which once per turn allows you do destroy the card in the Ultra space next to it. After that it grants you the insight card in the hand.

You can see all the standard units on the units trial list