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Don't do the companion PC. It's not necessary. If neither PC is a healer, just drop more healing potions. Encounter scaling will be different. On level (eg. 2 standards, or one elite, or standard + 4 minions) will work fine. However, when scaling up, the difficulty increases much faster. L+2 for 2 pcs is almost like L+5 for a party of 5. Also, don't use any action denial effects. Those can wreck a small party. Otherwise, just play as normal.It will take a little trial and error to get encounter design just right. When you throw a tougher encounter at them, be sure that there is an out if things go south. Eventually you'll have a handle on what works best. Just dive in and have fun!