Some abilities specify a time when you can activate them, like Eternal Dragons first ability or the opponent clause on Oft-Nabbed Goat
There are only so many key pieces to make Xander super impactful, and those cards have been known for quite some time now - cards like Bruvac, the Grandiloquent, Waste Not, or Conjurers Closet to name a few
The creature used in Voltron decks that are loaded up on is often your commander as, it is easy to get onto the battlefield, and you almost always have access to it
For example, if there are two +1/+1 counters on Aerith Gainsborough and it gets three -1/-1 counters, you'll put two +1/+1 counters on each legendary creature you control when Aerith Gainsborough's third ability resolves
You get all sorts of stories from it, like old-school players who remember (and sometimes regret) trading their moxen for a Shivan Dragon in the schoolyard
When the dust settles, youll still be ahead with five mana on turn four, with a sizable flyer and permanent Treasure tokens to start busting out your most dazzling spells