Como posso diminuir a dificuldade de uma cena em tempo real?

My party also prefers to see dice rolled in the open, so I've had to learn to creatively doctor encounters myself.

Change the Numbers

Instead of changing your rolls, change the numbers you're adding to the rolls or comparing the rolls to. If you feel you have to justify this, perhaps monster's so mad it takes a penalty to attacks and defenses, or the party has been given a temporary boon from the ghost of the monster's previous victim. Feel free to adjust hit points too: the only time the party has a sense of how many hit points the monster has left is when you declare it bloodied. If you change the hit point total before that point it's impossible to detect; if you change it after... the party probably won't notice and really shouldn't complain if they do.

Word of experience: If your party likes to use knowledge of dice rolls to extrapolate monster defenses and attack modifiers, they'll call you on this. Have a justification ready, or say "oops, let me check my math" and then move on to one of the other points on this list.

Fight Dumb

• Be less careful about getting flanked. Give the party a free +2 to hit!
• Provoke more opportunity attacks. Easy way to get the fight over faster. Don't forget that some circumstantial damage bonuses (like sneak attack) are per-turn instead of per-round, so combine this with the above point.
• Make poor tactical decisions, like triggering mark punishment when you don't have to. Defenders love it when you do that.

The other side of Fight Dumb is:

Meta Smart (reward your party for their choices)

• Use your debuff attacks against PCs who won't take it as hard (e.g., daze the guy with Superior Will).
• Take advantage of PCs traits to deal less damage. Set the tiefling on fire; he'll enjoy not caring. If a PC has poison resist, have the NPC take a small action to poison his blade (add the poison keyword to his attacks); suddenly the PC is taking menos damage and feels good about his resist choice.
• Target high defenses. Go for the cleric's Will, the fighter's Fortitude, the paladin's AC. Missing deals a lot less damage, and makes the party feel cool.
• Don't forget that trained knowledge checks can grant a PC limited knowledge of a creature's stats. Encourage this and reward it; perhaps the monster has a vulnerability they haven't been taking advantage of (perhaps you just made it up now!). I've been known to also grant small bonuses to attack or damage with knowledge checks, but don't make that a regular thing. Be creative with this one: maybe this particular monster can't make the enormous swings it's used to if its target is near blocking terrain, so it takes a penalty to attack PCs adjacent to walls. Or maybe the monster has poor peripheral vision and grants a +3 to flankers instead of +2, if you decide the party needs a bump in their to-hit?

Use Terrain

Before your next session, take look at the many terrain options 4e offers. Many of them can grant advantages and turn the tide of battles if used creatively, and they can inspire you to make your own terrain features as well. The crumbled remains of a holy shrine that gives a healing bonus to those nearby might be just what your fight needs; call for a Religion/History/Perception check to suddenly discover it in the middle of battle (maybe it lights up when a bloodied creature gets near?).

Don't Be Afraid to Call a Fight

Your monsters probably don't want to die. Some or all of them might surrender or run away when bloodied or when their friends drop. This shortens fights considerably, provides RP in battles and makes the world and its inhabitants more real.

Design Philosophies Have Changed

Around the time the Monstro 3 manual was published, 4e monster design underwent a drastic shift. Among other things, damage increased and hp dropped: this encourages faster, more intense fights. I don't feel competent to discuss the maths, so here are relevant posts:

• What updates should be done to older monsters to bring them in line with MM3 era monsters?
• Existem diretrizes para criar e personalizar monstros no estilo MM3?
• Como atualizar um monstro usando o D & D4 Monster Builder?

Confessar tudo

It goes against generations worth of the DM vs Players mindset, but you could just be straightforward with your party: You're a new GM and learning the ropes, and sometimes you're going to try things that don't work. You pode ask them to be understanding as you adjust things when you realize they don't work as intended, and you might even benefit from their direct input.

Well, in my opinion, fudging dice rolls isn't always cheating. This works as long as the GM's fudging contributes to the fun the group as a whole is having. If the GM is maliciously fudging dice to unjustly detriment the players, that's a lot different. I do, however, understand there are two sides to the dice fudging argument, and I understand where both are coming from.

My advice is to talk to your players and find out how they feel. I had this conversation recently with some players of mine. I said I'd like to try rolling out in the open, but providing them with extra resources with which to modify the results of die rolls (action points, hero points, fate points, whatnot). They preferred I rolled behind a screen and kept the actual result to myself, so that they'd have no clue when rolls were fudged or not and could focus on having fun.

I've had similar problems and experiences as a GM with years of experience. I think your gut instinct was right. There was a problem with the encounter and you intuitively knew how to fix it, but also made the right call in not 'cheating' the dice openly in front of the players.

What complicates the situation was that you were running the game online which always makes things trickier (in my experience).

I'd like to offer the following as advice:

1. Alter the Monsters: As @BESW already suggested, I recommend tailoring the monsters to suit your purposes. In some game systems, monsters are no more than various abilities, powers, and stats created solely by the GM. I make a lot of my own monsters, and most of the ones I use, I use customized.

Generally, it doesn't feel right to 'alter' monsters during an encounter. So, I think you did the appropriate thing there. However, as a newer(?) GM, I think you're well within your rights to improvise some new changes as you get the hang of gaming. With more experience you can put these changes in before the game. You can also let your players know beforehand that you'll be running your games 'off-book' which are often the best anyway.

2. Look for Hidden Rolls Feature: Most virtual tabletops have a GM Roll or Hidden Roll feature which you can use to keep your rolls secret. There are many reasons for using such applications including: fudging (cheating), stealth and spot checks, random monster encounter chances, and so forth. Really, there are many rolls the players shouldn't know about even if it's a simple 'detect lies' roll used on an NPC.

3. Simplify: Sometimes, the easiest thing to do is simplify and be creative. If the game is getting bogged down by too many dice rolls, modifiers, and statistics; simplifying things can often be helpful. This could be as simple as using a single d20 roll for 10 monsters or as elaborate as customizing the player's attack statistics.

4. Creatively Alter the Rules: While this might not work if you're just starting out, with more experience creatively altering the rules can do wonders for a game. In a similar situation, I would have done the following: boosted the Clerics hit rating and/or given him new special attack training/powers to make him competent in battle, Added more foes/stronger ACs to battle that tough fighter, and messed with the monster statistics to make them overall faster to defeat and more lethal in damage so they could heavily damage the party quickly, but also be defeated with a minimum of elaborate fuss.

That said, I do write and design RPGs, so that solution may not work for everyone.

Thanks for reading! I hope you find some of the above helpful in some way.