Muddle the Mixture 2: Augstralian Kangafrog

Up: A pretty good drop in red artifact decks.

Rose, Daughter of Armageddon 
Legendary Creature - Dragon Plant Avatar
As an additional cost to cast this spell, sacrifice a creature
Flying
When Rose enters the battlefield, destroy all lands.
With her every wing flap, a fertile land turns to waste.
4/4

Next: Narset, Enlightened Master + Commander's Sphere

Up: Neat take on Commander’s Sphere. However, it reads very clunky. A workaround for calling out color identity twice could be to just tap for , , or .

Eldritch Bond
Enchantment
Whenever you gain life, target opponent exiles that many cards from their library.

Next: Sword of Kaldra + Blightsoil Druid

Up: Nice muddle. A 3/3 for three mana in black definitely shoudn't be , especially not with "super deathtouch". You might consider one of the following:
• Make it
• Make it 2/2 and
• Make it and

Hunting Party
Sorcery
Until end of turn, target creature gets +1/+1 for each green permanent you control. It must be blocked this turn if able.

Next: The Ozolith + Frogmite

Up: That’s super neat. I just hope it’s not broken.

Trinket Guardian
Artifact Creature — Gargoyle
Flying
Artifact tokens you control have indestructible.
5/5

Next: Arbor Elf + Phantasmal Sphere

dangerousdice: You can put mana in your post by putting “::”’s around a letter, so :;U:: becomes , and so on

Up: Fun build-around card. Nice way of mixing those two cards.

dangerousdice you might want to take a look at the Planeswalker's Guide to Posting Syntax. You can turn cardnames into links by writing them between [card][/card] or you can put the link directly with [url=...][/url] around the text.

Vitalizing Sphere
Creature - Illusion
Cumulative upkeep—Untap a tapped land you control. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
When Vitalizing Sphere leaves the battlefield, target opponent creates an X/X blue Orb creature token with flying, where X is the number of age counters on Vitalizing Sphere.
2/2

Works a bit like Braid of Fire. You have to be able to use your lands during upkeep. Also it explodes if you don't have enough lands.
I was thinking about making it 1/1 with +1/+1 for each age counter, but that was a bit too much text for one card.

Next: Roil Spout + Savai Triome

Up: Pretty powerful card, as is to be expected of a free sac outlet. The closest I could find in each tribe was Sling-Gang Lieutenant and Cautery Sliver. I don't actually know whether either of those gets run by their respective tribal decks but this is an upgrade of both.

Mirrored Surface 
Instant 
Gain control of target spell that targets only an artifact you control. You may choose new targets for it.

Next: Scion of Oona + Vine Kami

Up: Interpreting the Vine Kami as plant wall is an interesting way of thought. I didn#t think there would be many cards this cares about, but 13 isn't actually that bad. Official cards usually let the creratures with defender "attack as thou they didn't have defender." It has the additional benefit, that you can still activate your Portcullis Vine.

Science Fair Defenders
Creature - Human Guardian
When Science Fair Defenders enters the battlefield and at the beginning of your upkeep, roll a d8. On an 8, roll two more dice. On any other result, put the indicated counter on Science Fair Defenders:
1 — -1/-1
2 — Defender
3 — Vigilance
4 — Lifelink
5 — First strike
6 — Flying
7 — +1/+1
4/4

A d6 just didn't have enough modes to satisfy my needs. Note that I put lielink on 4, as a nod to gaining 4 ilfe. (Also it has 4 power.)

Next: Amplifire + Dawnhart Rejuvenator