Actually after the recent hero buff, the progression should be:
50: +1 Magic
55: +1 Attack
60: +1 Life
65: +1 Life
70: +1 Armor
75: +1 Armor
80: +1 Attack
85: +1 Life
90: +1 Life
95: +1 Armor
100: +1 Magic
110: +1 Attack
120: +1 Life
130: +1 Armor
140: +1 Life
150: +1 Armor
160: +1 Armor
170: +1 Magic
180: +1 Life
190: +1 Attack
200: +1 Life
225: +1 Armor
250: +1 Magic
300: +1 Attack
400: +1 Armor
500: +1 Magic (card becomes Mythic)
750: +1 Life
1000: +1 Attack