Ryu - Hiryuu Fist Mode
This is Capcom's way of making up for not putting Ken in. Ryu can now transform to use Ken's set of moves. He gains Ken's speed which is a useful thing for this game, but he doesn't get the stronger special attacks that Ken has. The Tatsumaki Senpu Kyaku can not almost kill an opponent when used as a air combo ender like it does in Marvel vs. Capcom 2. This comes in handy for the opponents, but falls as a disadvantage for the user. Ryu's standing MK and FK have changed to Ken's, but the air MP has not which can end up providing another problem for all of the Ken combos that were formed a long time ago. If you like Ken, then you should use this form, otherwise, don't bother since it's a waste of effort.
Special Attacks
Hadoken - QCF+P
Shoryuken - DPM+P
Tatsumaki Senpu Kyaku - QCB+K
Super Attacks
Shoryu Reppa - QCF+2P
Shinryuken - QCF+2K
Shippu Jinrai Kyaku - QCB+2K
Shotokan Mode Morph - HCB+WP
Shin Shotokan Mode Morph - HCB+FP
Combos
D+WK, D+MK, QCF+2P
Do 2 crouching kicks and then cancel them into a Shoryu Reppa.
D+WK, D+FP, QCF+2K
This combo really only consists of a launch into a Shinryuken. This can do some massive damage, but if the Shinryuken not cancelled quick enough, it'll only do 1 hit and the opponent will be able to hit you.
WK, MK, QCB+2K
First, hit them with the WK to set up the MK. After you hit with the WK, cancel that into a MK, let it hit for the full 2 hits. Cancel the 2nd hit of the MK into the Shippu Jinrai Kyaku as soon as the 2nd hit actually hits. If you wait even a split second too long, the combo won't link. (After you hit with the Shippu Jinrai Kyaku, you can cancel into the Shoryu Reppa before he carries them up into the air. After 2 Shryukens on the Shoryu Reppa, you can then cancel it into the Shinryuken to end dealing massive damage.)
FF+WP, FP, QCF+WP, QCF+2P
This is almost the same as the Shotokan form combo, only this time you have to cancel out even faster than before. If you don't cancel out in time after the weak Hadoken, the opponent will have the chance to block and most of them will use that chance.