The new rules make it much simpler
There are currently 250 base cards in Pokmon TCG Pocket, including 226 cards you can get in Genetic Apex, and 24 Promo cards you can grab in Pokmon TCG Pocket during in-game events, like the Wonder Pick event that's ongoing at the time of writing
Assess the situation and if it justifies interrupting the combo and attacking with Lucario to deal with a big attacker, then do so
The back face of a transforming double-faced card usually has a color indicator that defines its color
A standard smartphone is roughly 3 to 3.5 times taller than a Pokmon card and about twice as wide, depending on the model
Every other timing rule for casting spells still applies: If the mayhem card is an instant, you can cast it any time you have priority that turn, but if it's a creature you can only cast it at sorcery speed (unless another effect gives it flash)