It's cheap (mana-wise), it's fast, it lets you get back an instant or sorcery in your graveyard, and it's a 2/1 body that can attack and defend just like any other 2/1 body
While she pairs well with flash, Elsha relies more on top-decking your cards so you can surprise enemies with lightning-quick casts of powerful noncreature spells
Special Resource Points - Some characters have special resource points
Defensive phase-outs like Teferis Protection also allow creatures to dodge boardwipes, edicts and other non-targeted removal, where many flicker effects simply return them to the battlefield in time to perish by the next spell you had been responding to on the stack
Take a rough sketch (budget, power level, theme, playgroup) and use tools like Scryfall to filter 2,000+ legends down to candidates
The other two sites are great for players who want to print a bunch of Magic cards, likely to proxy out an entire deck