If you have a card in your hand that says Evolves from so-and-so and so-and-so is the name of a Pokmon you had in play at the start of your turn, you may play that card in your hand on top of Pokmon so-and-so
As a suggestion, try to keep them relatively simple
Amazoness Onslaught X TRAP Continuous Once per turn, during the Battle Phase: You can Special Summon 1 "Amazoness" monster from your hand, and if you do, it gains 500 ATK until the end of this turn (even if this card leaves the field)
As cards start getting to be over $100, they become much rarer in packs, meaning you'll have to be lucky to see them
Strength aside this type of "whole table interaction" is quite fun and I think most players would enjoy it - Even if they do end up getting overrun by a scurry of Squirrels
While its probably a decent budget Commander card, it only goes for $1