Speed How likely your Pokmon is to attack first
Lets name some of them: zombie support, fusions with Summoned Skull and Meteor Dragon , the early 2010s meta-defining Red-Eyes Darkness Metal Dragon , XYZ retrains (some of which can cause funny infinite combos), and more
Not only is buffing up a creature before having it fight an opponents creature a potent trick, but you can play it at instant speed
Geomathmech Magma When this Tuner Synchro Monster destroys a monster by battle, you can destroy up to 2 cards on your opponent's field
I've barely mentioned half of them, with further objective types, event objectives available for limited time - but again, very generous and doable challenge - letting you pick up some special cosmetics like playmats and card covers