dhc glitch is basically a glitch in the dhc that allows you to whiff a hyper to reset the damage and hitstun scaling. this allows extremely damaging combos and you build extra meter because you are doing a normal combo again. a normal dhc wont reset damage and hit stun so using this glitch will allow you to do stronger combos.
this glitch usually occurs during dhc from a capture (animation) hyper or performing a hyper during a captured state (magneto's hyper grab, tron's serve bot gun, etc.) into a power-up or counter hyper. this glitch is removed anyway so it wont matter anymore.
are there any characters in UMVC3 that you could recommend for me?
there are characters like wolverine, hulk, nemesis, sentinel, ghostrider, dormammu, wesker, and of course dark phoenix, who hit very hard and requires minimum execution skills. but the majority of them except wolverine, wesker, dark phoenix and dormammu are very slow and will lose to fast zoning characters like dr doom, dante, zero, wesker, storm, magneto, etc. without proper assists to help them get in. or you can try someone like arthur, who has a lot of projectiles but a little combing ability and just spam chucking weapons all day.
my advise would be try to do everyone's missions and all their moves in training mode, and most importantly learn how to move around with them effectively, and see what you like best. but my guess is hulk and sentinel are probably the best for you, because their combos are extremely easy and they have powerful command throw and armoured moves to help you get though. plus sentinel drones assist is good for everyone. and just follow my guide to pick a top tier if you are unsure who to pick after you picked your favourite character and you need someone to fill in the slots.
btw, i have mastered the desk nemesis relaunch combo and i have a new relaunch combo with hulk using both assists to deal 980k damage with only one meter and no dhcs!
if you are unsure on how to use assists, you should just think of it as a extension of your special move list and better yet, you can block and move around during this "special move". for example you can call the drone with hulk and jump in and hit them with an attack, so they will have to block your attack because the drones are coming. during this time you are free to attack them again or command throw because the drones are still there and it will stuff their attempt to strike back.