It's arguably the most popular gimmick the game series has released, so to have it back in the TCG is an immediate win in my eyes
This gives you a blocker on the field to protect your Leader or a rested Character, but it can also prevent opponents from attacking a Character you just attacked with
Nagashimas favorite strategy, though, is one he himself was heavily involved in designing: the infamous Night March deck, which dominated much of the competitive scene in 2016 and won the US Nationals that year
The only other cool thing to note about the deck is how brutal the Urborg, Tomb of Yawgmoth is in combination with Sundering Titan
It can tribute two monsters to inflict 1500 damage on your opponent, making it extremely easy to blow out your opponents entire game plan
The best Pokemon TCG Pocket ex Starter deck is probably the Dark-type Paldean Clodsire ex deck, at least at time of writing, but in reality the answer is a lot more complicated than that