Jump Ultimate Stars

A useful deck you could get soon for that mission could have:
Killua 5
Train 4
Trunks 3

Just spam Killua's Y, Train's ^X and Trunks 3

Take gohan and spam fire balls :)
Or Rao

I used Bankai Ichigo and stand exactly next to Muhyo and spam with Y which creates sort of a "force field" because if enemies touch it they get hurt and if they do a long range attack it wont reach Muhyo. and sometimes Muhyo uses a support character which prevents eniemes from moving

For some reason, if you don't stand anywhere close to Muhyo, none of the CPU's should touch him. It's happened to me. Otherwise, just create an super special awesome combo, one that you can create in the beginning. My super special awesome combo is the sanji paralyze combo. Get that chick from saint seya, the one who has a straight 3 block and paralyzes the opponet with some swirly thingy. Build it in a deck with 6 koma sanji. Make sure to make the swirly girl "R". As soon as you do sanji's spinning kick attack, activate your X special and press R. The opponent should get paralyzed and stay paralyzed until the combo is done.

Easy. Use Killua 5 and any movement stop (not necessary) or sena 2 or 3 for confusion or movement stop and get them together and just click >b over and over.

Use kenshin 5 or 6 and his normal x attack

First I got to the right Muyo before the start and used Luffy and his forward Y to snap the guys back. Should be able to hit both at the start. Then keep using forward Y to keep them on the wall.

Or use majin buu and do >y for the foot thing and try to keep them cornered.i think the enemy will attack whatever is closest to them and keep em in your screen and away from muhyo.

Get Luffy's 6 Koma (Afro luffy as i lije to call him) along with seiya 3. Spam Luffy's normal X and keep them cornered, if the enemy gets side by side with u use seiya get behind them and normal X Luffy :].

Try to stay next to him for the longest time that you can. He will block by himself when needed. If you have a character with a Special that goes around you as well, that works best.

use 6square taikoubou up X in the middle of muhyo

It's easy. Muhyo goes to the bottom of the stage at the begining of the match, go down there with him, the enemies soon follow. If they are seperate try to get both of them to one side by getting behind one of them and doing a powerful attack that will send them flying to the other side of Muhyo (all the while Muhyo has been keeping up his blocking). Now just keep doing combos to both the cpu's until time is up (or until the specified times are up).

it's very easy.This is what I idid. Just pick people who is good at long range and stand next to Muhyo. After 30-40 seconds go close combat and go away from Muhyo and they will come after u.