I've never really allowed multiclassing...I view it as an excuse make ridiculously broke characters. However, my players always wanted multiclassing in our games (half of them are basically munchkins that just love making the strongest characters possible).
After so long, I was thinking of just giving them a Christmas present of allowing multiclassing.
Is it a good or a bad idea? What should I be on the lookout for? What should I be careful about? Tips?
Thank you
Not an optimizer myself, but I have noticed a few general tips on here, to lower the number of broken characters.
Do not allow feats WITH multiclassing, or at least not the big contenders (Polearm master, GWM, Sharpshooter, Crossbow expert, I think are the usual suspects.)
Warlock and Fighter make insane dips, with Action surge and Short rest spells, plus the Eldritch blast cantrip.
Be careful about magic items. For example, say you allow the feats listed above, and have a Barbarian/Fighter with GWM. Do you really want him to have a magic Great sword, or battle axe?
That is all I have for now, you will need a real optimizer to get a list of dangerous class combos from.
EDIT: I forgot to mention the upside. You can powergame too. Throw some dangerous stuff at them. A Bugbear gets really scary with an Action surge, or sneak attack. Don't play so hard you invalidate their own work they put into powergaming, but let them feel the pressure every now and then, that they are still not the strongest thing around. Keep them on their toes, and have fun with it.