If their strength is lower than their willpower, they take damage and damage counters equal to the strength value are placed on the card
Alternatively, attending local trading card events, and conventions, or visiting dedicated Pokmon card shops can provide opportunities to buy, sell, or trade Rainbow Charizard cards in person
Credit: Wizards of the Coast Alesha, Who Laughs at Fate Marcy: Assuming you can keep Alesha on the field and growing, or grow her before damage is calculated, you could probably pull some fun Rakdos graveyard shenanigans here
You can for example visit Keyrune by Andrew Gioia
Whether its due to the amazing artistry and illustration of the card itself, its potential power in the competitive scene or overwhelming nostalgia, there are a lot of reasons why certain cards become more valuable than others