There are a few factors that go into determining the value of your cards
In the one-mana slot alone, Mother of Runes, Giver of Runes, Benevolent Bodyguard, Zack Fair, and Skrelv, Defector Mite all work to protect Cloud when he comes down
Dan and Tom were both phenomenal contributors, spending hours and hours playtesting cards, organizing a huge amount of decks, and providing feedback on which cards were too strong and which cards weren't strong enough
For most active interaction, you'll need to wait for the spell to resolve before you can do anything
In other words, you have to activate or cast the ability or spell that grants regeneration at a time when you have priority, or under some condition spelled out by a static ability regenerates text