The guided game is a fairly effective introduction to the concepts
For kids, its exactly how it should be , meaning theyre not almost always wasting $4 of allowance on a pack containing nothing but bulk
Marvo, Deep Operative Marvo, Deep Operative is an interesting one from Murders at Karlov Manor Commander at least
For example, if you control The Ozolith ("Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.") when Sin's last ability resolves, you'll put the appropriate number of each kind of counter onto both The Ozolith and the target creature
For fast decks that want to get their game plan in motion off the rip, drawing five cards with one Trainer is a huge jumpstart, especially with Carmines added benefit of being usable if youre going first