With the froghemoth, we witness another one of the authors’ odd classification decisions: the flavor text describes froghemoths as “creatures not of this world,” who first emerged from “strange, cylindrical chambers of metal buried in the ground,” but they’re categorized as monstrosities, not as aberrations. Then again, it may not matter much, since even aberrations behave as evolved creatures—they’ve simply evolved in conditions too alien for humanoids to comprehend. And monstrosities should always behave as evolved creatures unless there’s some specific reason to think they shouldn’t, such as being created through some kind of fiendish curse.
Pure brutes, froghemoths nevertheless have proficiency in Stealth, indicating that they’re ambush predators. If at all possible, they hide underwater and strike with surprise. Once they’ve attacked, however, they overwhelm their opponents with their extraordinary Strength and Constitution.
I notice two details tucked into the top half of their stat block. The first is that they have proficiency in Constitution and Wisdom saving throws—two of the big three—but not in the third, Dexterity, and their Dexterity is above-average but far from extraordinary. In general, therefore, they’re not afraid of spellcasters per se. But a spellcaster slinging damaging Dex-save spells will annoy them greatly, and in particular (this is the second detail), lightning bolt or any other spell dealing lightning damage will alarm and enrage them.
The froghemoth’s attack pattern is surprisingly complicated. It has a conditional Multiattack: it gets two tentacle attacks, plus either a tongue attack or a bite attack. The tentacle attack grapples on a hit, but importantly, it doesn’t also restrain. This means that grappled opponents suffer no disadvantage when fighting back (at least, not because they’re grappled), and the froghemoth gains no advantage when attacking them. It also means they can still take any action, such as Use an Object, Cast a Spell or even Dodge, that doesn’t involve being someplace else.
The tongue attack pulls but doesn’t grapple. In other words, it lets go as soon as the target is pulled up to the froghemoth’s mouth, whereas the tentacle attack holds on—and, it’s worth noting, doesn’t pull the grappled target, at least not automatically. A grappling creature can drag a grappled target (Player’s Handbook, page 195), but this would involve either moving or using an action. In general, therefore, we have to assume that a target grappled by a froghemoth tentacle is simply held in place.
However, it just so happens that the range of the tentacle attack and the range of the tongue attack are the same. So if a froghemoth has a victim grappled by a tentacle, it can then use its tongue to slurp that victim toward its mouth. And a successful tongue attack also includes a bonus bite attack action. So really, it’s not a choice between tongue and bite—it’s a choice between tongue-and-maybe-also-bite and bite-and-nothing-else.
Like a giant toad’s, a froghemoth’s bite attack swallows its target on a hit. Unlike a giant toad, a froghemoth can digest two targets at a time. We can assume that doing this is its overall goal.
Froghemoths are stupid, but they do have Wisdom 12, which we have to interpret as a level of survival instinct or animal cunning sufficient for it to recognize who’s good prey and who isn’t. The best prey is whoever has the least armor and the lowest Strength modifier, and the simplest way to rank your player characters and non-player characters is to add these two stats together. Whoever’s on the bottom is the froghemoth’s most favored ration.
Will a froghemoth wait until its preferred targets are in range, though? Not necessarily. While it may not necessarily want to eat a strong, armored-up character, it still gains some benefit from grappling them and holding them out of reach. Since it attacks from hiding with advantage—or at least expects to, since most prey won’t notice it lurking—it will strike with its tentacles as soon as two or more opponents stray within its 20-foot reach. It will always grab at the closest one first; whether it hits or misses, its second tentacle attack will be against whichever target in reach has the lowest AC + Strength mod.
Now the heuristic gets complicated, as we have to use math to represent the froghemoth’s instinctive judgment. The froghemoth has a two-thirds chance or better of hitting a target with armor class 17 in one attempt or of hitting a target with AC 14 twice in two. It also has a two-thirds chance of reeling in a character with a Strength of 17 or lower with its tongue. (Dexterity modifiers? Saving throw proficiencies? Froghemoth no los comprende. When you calculate AC + Strength mod, do not include a character’s Dexterity modifier in his or her AC, and use raw Strength modifier, not Strength saving throw modifier.)
If there’s a character already within 5 feet of the froghemoth, and he or she is wearing anything but plate mail (or chain or splint, if the character also carries a shield), the froghemoth uses its bite attack against that character.
If the froghemoth has one or more characters grappled, it make a tongue attack against the one with the lowest AC + Strength mod, but only if that character’s AC + Strength mod is less than or equal to 15. (To make it easier on yourself, calculate the AC + Strength mod of every character in your party and sort them low-to-high before this gaming session starts.) If the tongue attack succeeds, it follows up with a bite attack.
Starting in round 2, the froghemoth extends its attention to every character in the area. Including those it already has grappled, who’s got the highest AC + Strength mod, and who’s got the lowest? From this point on, the froghemoth will ignore the character with the highest AC + Strength mod (unless he or she is already grappled, in which case the froghemoth will simply hold on) but will pursue the character with the lowest (unless he or she is already grappled, in which case the froghemoth will attack only targets currently within reach). Remember that the froghemoth is not slowed to half speed if it’s carrying a grappled opponent in one of its tentacles, because it’s a Huge creature.
What if the froghemoth has already caught the character with the lowest AC + Strength mod? Then it becomes a matter of whether it’s easier to catch someone still running around or to simply swallow whomever it already holds in its tentacles. As previously mentioned, a grappled target makes a good meal if its AC + Strength mod is less than or equal to 15. For a free target, the standard is even stricter: an un-Dex-modified AC of 14 or lower for a character with Strength mod −2 or −3; 13 or lower for Strength mod −1 or 0; 12 or lower for Strength mod +1 or +2; and 11 or lower for Strength mod +3. (Again, do the math before your players show up. You’ll be glad you did.)
Now, what about that lightning damage? Lightning staggers froghemoths, denying them their Multiattack and halving their speed. A froghemoth that’s just taken lightning damage will freak out. If the character who dealt the damage is running loose, it will drop everyone it’s holding grappled, move straight toward that character (at half speed) and try to either bite it or grab it with a tentacle (the only action it gets). If the character is already grappled, the froghemoth will use its movement to close the distance and bite.
The froghemoth is debilitated for only one turn unless it takes additional lightning damage, but just that one instance rearranges its priorities. It’s on a rampage now, and it’s not going to be happy until whoever dealt the lightning damage is in its belly—unless that lightning damage reduced it to 73 hp or fewer. Actually, any damage sufficient to reduce a froghemoth to 73 hp or fewer will drive it away. Using the Dash action, it retreats into the water . . . oh, but I didn’t say anything about its letting go of the folks it’s holding in its tentacles, did I? It’s so dumb, it forgets to do that, and it drags its grappled opponents into the water with it. Hope they can make their escape rolls before they run out of breath.