I say trade-in (at least 2) definitly because he has 6 lvl 8 monters (horus 8 and silent mage 8). And to add, he use level modulation, so this is how it works: dump silent mage or horus for trade in, use level modulation to special summon what you just dumped. plus you get 2 new draws woohoo! So -2 mallets and +2 (or 3) trade-in and +1 horus 8.
For gladiator beast, in my oppinion, is the scariest deck ive ever faced (with my dragon deck). Once he gets you with the tag in/tag out, contact fuse, destroy 2, contact out, special summon 2, contact fuse again, negate magic/trap by discarding 1 card, etc..... all without using magic cards or trap cards. So what if you make magic cards useless or have royal decree out? That wont stop gbs, trust me. what does stop them, or even most decks youll see out there, is solemn judgement. Bottomless trap hole is also another card thats versile that stops most trumph cards in any deck (like DAD). But dont get me wrong, im not saying that GB is the most popular or strongest deck out there... its just that running only 3 royal decree will not give you more advantage than running solemn judgements or bottomless traphole or other good trap cards.
I like your deck so far though, seems fun :).