What do planeswalkers earn on level ups?

Each level up, a planeswalker unlocks something new. It's often 4hp, additional mana per color match, or a leveled up ability.

Here's what I have so far, tested only with Chandra:

• 2: 1st ability is now lvl 1
• 6: 2nd ability is now lvl 2
• 14: 2nd ability is now lvl 1
• 26: 3rd ability is now lvl 1
• 31: +4hp
• 32: 3rd ability is now lvl 2
• 33: Your planeswalker regeneration improved
• 34: Your planeswalker regeneration improved
• 35: Your planeswalker regeneration improved
• 36: +4hp
• 37: Your planeswalker regeneration improved

Is there a comprehensive list somewhere?

The information is not quite complete, but there is a crowd-sourced spreadsheet linked on the D3 Go! forums. There's a little too much information to list everything here (49 levels * 5 planeswalkers) not to mention any future planeswalkers that may be released.

However, the ability unlocks are fairly consistent across all 5 planeswalkers:

• 2: 1st ability, lvl 1
• 8: 1st ability, lvl 2
• 14: 2nd ability, lvl 1
• 20: 2nd ability, lvl 2
• 26/27: 3rd ability, lvl 1
• 32/33: 3rd ability, lvl 2
• 38: 1st ability, lvl 3
• 44/45: 2nd ability, lvl 3
• 50: 3rd ability, lvl 3