I’ve been having some fun playing on MTG Arena and Radiant Fountain has given me an idea for a new card design.
“When land enters the battlefield, draw 1 card”
“Tap to add one colorless mana to your mana pool”
I don’t think it’s too powerful as is, even for Standard. With the power creep a lot of standard legal cards just automatically replace themselves as it is. If it is too powerful you could just add “enters the battlefield tapped”. In either case I don’t think the card would warp any format but it would be a decent card.