RMA: Oliphaunts (Elephants and Mastodons)

I can stand the sight of worms,

And even microscopic germs,

But technicolor pachyderms,

Are really too much for me!

                                     -"Pink Elephants on Parade"

It's hardly surprising to find that elephants are pretty formidable opponents in D&D. They're big, they're strong, and they basically have SPEARS coming out of their faces. I have rarely seen them in play, though. Elephants –and their prehistoric cousins, the Mastodon– are rare on random encounters. Each only appears a single time (Grassland and Optional: Prehistoric) on the charts. Nevertheless, "modern" elephants are sometimes tamed in certain cultures and can make for an interesting encounter.

aka "The last thing Uncle Ted saw 

after setting off a firecracker on safari."

Elephant (from Cook)

AC: 5 

HD: 9

Move: 120' (40')

Attacks: 2 (tusks) or 1 (trample)

Damage: 2d8/2d8 or 4d8

No. App: 0 (1d20)

Save: F5

Morale: 8

AL: N

First of all, up to twenty in a herd. Secondly, NINE hit dice. Their AC is decent, too. If you tick these things off, you have some heavy work ahead. 

They charge to start with, doing double damage with tusks, so that's potentially sixty-four hit points of damage right there. THEN they start trampling for up to 32 points per attack. Those 9HD means elephants hit often enough, but check this out: Against man-sized or smaller, they get a +4 to attack!!

Mastodons are pretty similar, except tougher (though they deal slightly less damage with their tusks).

Mastodon (from Cook)

AC: 3 

HD: 15

Move: 120' (40')

Attacks: 2 (tusks) or 1 (trample)

Damage: 2d6/2d6 or 4d8

No. App: 0 (2d8)

Save: F8

Morale: 8

AL: N

The best way to deal with either of these creatures as foes? Scare them off. They're herbivores with so-so morale. Just don't be in the way when they stampede in a panic. 

The tusks of these creatures are valuable enough to entice some to take the risks (up to 800gp per). Hooks involving ivory hunters, vengeful druids, and elephant graveyards full of tusks could make for a fine adventure indeed!

RMA: Rhinoceroseseses

(Rhinoceri?)

Like many other real creatures, this one hasn't seen a lot of table time in my experience. In fact, the normal rhino doesn't even appear on the random encounter charts; and the wooly version is only on the optional "Prehistoric" table.

While, in real life, rhinos are hardly racking up the kills (much more the reverse, actually), they are notoriously unpredictable. Looking at the stats and descriptions, it's totally understandable why PCs might give this fellow a wide berth.

Rhinoceros       Ordinary        Woolly  (from Cook)

No. Enc.:        0 (1d12)          0 (1d8)

Alignment:      Neutral           Neutral

Movement:     120' (40')         120' (40')

Armor Class:  5                    4

Hit Dice:        6                     8

Attacks:                  -butt or trample-

Damage:        2d4 or 2d8       2d6 or 2d12

Save:            F3                    F4

Morale:          6                       6

What the scariest thing about its stats (either version)? No, not the trampling damage. Give up? The answer is its morale! I know, but it's a trick question. You need to read the description to see why.

"If threatened, surprised, or charged, they will stampede in a random direction, goring all in their path for double damage on the first attack."

Get that? These suckers spook 50% of the time, then proceed to go barreling off who knows which way. Even if you are what scared them, they might come at you instead of fleeing. You can't predict it. If they happen to head your way, their gore attack deals 4d4 or 4d6 damage, depending on type. You are almost certainly dealing with several of them at once as well. Imagine a half dozen of these things thundering at you!

Once that first gutting is over, the things might stick around to finish the job. With 2d8/2d12 for stomping you into the dust, it might not take very long either.