D&D 5E: unlearning old ways and more rulings not rules

Last post I mentioned how we were less than spectacular in our last two encounters.  Well it turns out that further led to us being overrun by the rest of the current inhabitants who were not pleased we broke into their stronghold.  The entire evening was combat and searching post combat (kill things & take their stuff).  A number of interesting rule related questions came up.

I noticed another player counting diagonal squares in the 1-2 method we used to use in our 3.5E game.  Turns out we never asked the DM how he wanted to run tactical grid movement.  Half of us were doing 1-2 diagonals and the other half were not.  Oops.  DM ruling - no extra cost for diagonals.

We were hit from two directions by opponents.  The wizard chose to place a flaming sphere in one of the doorways to hold them off while we focused on the other attackers.  Questions came up: is the sphere solid, what kind of cover does it provide, can creatures run through the sphere, does it do damage if they do?  On the spot DM ruling - no ruling on solid, provides half cover, creatures moving through the sphere itself would take damage, and we'll sort this out between games.

Due to the party not really working together here, we end up with a fighter surrounded by enemies in a nearby room.  We previously learned the hard way about having two or more hobgoblins next to one of our folks.  The wizard planned to rush in and blast away with burning hands but before his turn a hobgoblin places himself in the opening apparently foiling that plan.  Or so the DM thinks.  My rogue has an inspiration coin and this is a great time to use it.  I draw a dagger and throw - advantage roll gives me not only the hit I needed but a critical hit, which with sneak attack is enough to take him down.  The wizard executes his plan, which takes down enough opponents so the fighter survives and takes out the rest.

Feeling like we were about to be overrun (feeling was correct), we prepared to flee.  Fortunately, the team did think about holding a door closed against oncoming onslaught.  Sadly, the weaker of our two fighters who was already hurt and our wizard decided to take on the task.  Well, to make a long story short, they were overrun.  An opponent (no spoiler since we are playing Lost Mine of Phandelver) appears in the doorway and on shots the wizard, the DM says they used stealth to get to the spot which is how it got advantage.  We shake our heads on that one, unless we did not understand the terrain we did not see how that was likely.

Now the hurt fighter was surrounded and contemplating using disengage to move away when I asked if he considered using dodge.  Dodge?  Seems like he never understood this action was available and in the first time in about six sessions someone on our team took the dodge action.  So he decided dodge it is, and stayed in place to avoid opportunity attacks until (presumably) the rest of the party came to rescue him.  Man of faith this fighter must be.

My rogue comes around the corner and sees the new mess we are in.  When I last saw my group things were not so grim.  That is what I get for going into another room to get some treasure.  I decide to use my invisibility potion and figure I will wait for a chance to feed a healing potion to the wizard when the bad guys are focused elsewhere.  I move into position.  Our cleric remote cures the wizard, who feeling desperate pulls out a fireball scroll, makes his roll, rolls statistically improbably damage and toasts all the bad guys leaving only the most powerful one left standing.  Sadly for me, being invisible, the wizard does not know I am there and I enjoy a good toasting too.

Now we questions, what happens when an invisible character goes to zero hit points?  Look at the spell and it requires concentration.  I had not even considered that, and had not even considered a potion might require concentration from a non-spell casting.  DM ruling, I become visible.  Which turns out to be convenient for me because other wise they could not find me to fix me up.

But now this really begs the question: are potion spell concentration requirements the same as casting a spell?  And would that mean you could only have one potion active at a time which requires concentration?

Stay tuned - the dice never lie.