By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging encounters against a Giant Frog
Note: This has been prepared utilizing only the 5E Core Rules. The Giant Frog can be found in the Monster Manual page 325.
Giant frogs are medium sized beasts that live in wet or swampy environments. While their size has been defined as medium, because they can swallow a small size opponent whole, it is likely that they are on the larger side of that size range. I suspect that they are probably at least five feet tall.
Giant frogs come in many colorations and general varieties, almost as many as their smaller natural cousins. While we typically consider the giant bullfrog, almost any species of natural frog can have a giant version.
Step 1) Let’s Review what we know about Giant Frogs:
Giant Frogs have above average strength and dexterity, and average endurance. Giant frogs have a normal sense of self preservation, but only animal intelligence.
Giant frogs have an instinct that gives them proficiency in Perception and Stealth.
Giant frogs have Darkvision 30-foot and a Passive perception of 12.
Giant frogs are amphibious having the ability to breathe both air and water.
Giant frogs moving on land have a 30-foot walking speed, in the water they have a 30-foot swim speed.
Giant frogs can make a Standing leap forward of up to 20 feet forward and 10 feet up. Note that this is part of their MOVEMENT and thus does not count against their actions. A frog making a standing leap is vulnerable to attacks of opportunity only from opponents against which they were engaged and broke contact, opponents passed on the path of their jump do not get attacks of opportunity.
Step 2) Determine the probable Strategy/Tactics
As beasts, the giant frog will typically wait, motionless, until a prey animal comes within its attack range. It will then “Bite” by lashing out with its tongue. If the creature is small enough, the frog will attempt to wrap (grapple) and draw the prey in to eat it, swallowing it whole and digesting after consumption.
Step 3) DM Tips and Observations
It is my opinion that any animal that has a ‘GRAPPLE’ as a primary attack should have greater strength, I would increase this to 14, with an escape DC of 12.
I define the BITE attack from these creatures as a ‘tongue slap’, that than a tooth chomp. I would give them an attack distance of 10-feet vs the 5.
If the frog is hiding and concealed by environmental debris, then half-cover gives a bonus of +2 to its stealth roll, three quarters cover gives a +5 bonus to its stealth roll.
If the frog attacks from hiding, it has advantage on its initial attack.