Questions for a campaign

[Blackwing687]

I am a newer DM and I had a question well a couple really and I could use a bit of help or advice. My one group of six LVL 5 players is heading into a cavern chasing after a Bandit Captain(CR2) and Vice Captain(CR1) (Vice captain I made an in between the Bandit and Bandit Captain). What they don't know it that a LVL 5 Rouge Arcane Trickster in down there too. I have the idea of having the rouge use minor illusion to create a stalagmite and hide in it (other real ones will be around). The two bandits will go to either side of it and fight in those positions. The rouge in my mind can then use sneak attack damage on them from within the stalagmite. Perception check DC 20 to see if they can catch a glimpse of the blade returning into the rock. This is the scenario thus far. My questions are
1: Can a rouge trickster actually hide and attack from within the minor illusion without it breaking the spell? (I have read the spell and am under the impression that it could work)
2: What would be the EXP for the Rouge Arcane Trickster if defeated?
3: Would this be a decent challenge or too much? They have just taken out a medium sized group of 2 scouts, 3 mastiffs, and 7 bandits.
I was thinking of adding a few more bandits if it was not challenging enough given the amount of real stalagmites around there should be a decent amount of coverage for them to ambush.

Thanks for reading and any advice would be welcome.

[Specter]

1) yes.
2) probably as a CR3 creature.
3) Even with the earlier encounter, it strikes me as too easy. With 6 in the party, they could just 2-on-1 those guys and probably be done in 2-3 rounds.

[Ninja_Prawn]

Yes, but the PCs will figure out pretty quickly that it's an illusion. I mean, if someone is stabbing out of it... yeah, they're going to see that and the illusion will be foiled. At the same time, hiding is not actually necessary to get sneak attack if one of the rogue's allies is in melee with a PC.
You'll need to work out its CR. Typically monsters with PC levels come out with lower CRs than their ECL, mainly because they have so little HP.
Assuming the rogue comes out at about CR 3 as Specter suggests, the total encounter is worth 2,700XP. That's almost a 'medium' encounter for 6no 5th level PCs, which means it will likely end up pretty easy. Adding a couple of bandits may well be the right move.

[CaptainSarathai]

CR is really easy to figure out; base CR is roughly equal to 4 characters. So a CR3 creature is "fair" for four Level3 characters.

For character levels, I'd work CR as being 1/4 of their level. So, your Rogue is gonna be CR1.

Honestly, your fights are too easy. You're not burning off enough resources. You need to either have 6-9 encounters per day, or you need to have 3 very deadly ones.
The DM's guide is very much about math. You need to work within those guidelines until you have a good grasp of how your party handles them, and then you can start modifying things a bit to fit your taste.

[Sir cryosin]

Ya this encounter is only going to last one round.

[MrStabby]

There are a few easy things that can toughen it up. Spell scrolls, healing potions and similar.

Arcane tricksters can use mage hand to trigger traps.

Sounds like you might have a lot of difficult terrain that can make good killing fields for bandits with Longview.

[Blackwing687]

Thanks everyone I now have a bit of a better understanding of the situation. I was able to burn a few heals from the cleric and a 3rd lvl spell from the bard they have a tendency to just rush into things and given your feedback I now know why. I had a feeling things were a bit too easy for them but wasn't sure on how to go about things. I have gone through some of the dm manual but not it all I am going to give it a real good read though as I found how to lvl and change and check monsters and npcs. I am thinking of leveling the rouge and Bandits (captain and vice captain) set a few traps add a few underlings and potions I just have to make sure I remember everything lol. Thanks again anymore advise is always appreciated.