diff --git a/Makefile b/Makefile
index 9fa39d99..a0f181f7 100644
--- a/Makefile
+++ b/Makefile
@@ -87,7 +87,7 @@ endif
 
 # ditch g3, we aren't using that in GCC
 ifeq ($(COMPILER),gcc)
-  OPTFLAGS := -Os
+  OPTFLAGS := -Ofast
 else
   OPTFLAGS := -O2 -g3
 endif
@@ -339,12 +339,18 @@ build/src/libultra/os/%.o:    OPTFLAGS := -Os
 build/src/libultra/rmon/%.o:  OPTFLAGS := -Os
 build/src/libultra/debug/%.o: OPTFLAGS := -Os
 build/src/libultra/host/%.o:  OPTFLAGS := -Os
-build/src/audio/audio_load.o: OPTFLAGS := -O2
-build/src/audio/%.o:          OPTFLAGS := -O2 -g
 
 # per-file flags
-build/src/libc_sprintf.o: OPTFLAGS := -Os
-build/src/libc_math64.o:  OPTFLAGS := -Os 
+build/src/audio/audio_load.o:      OPTFLAGS := -Os
+build/src/audio/audio_heap.o:      OPTFLAGS := -Os
+build/src/audio/audio_effects.o:   OPTFLAGS := -Os
+build/src/audio/audio_general.o:   OPTFLAGS := -Os
+build/src/audio/audio_playback.o:  OPTFLAGS := -Os
+build/src/audio/audio_seqplayer.o: OPTFLAGS := -Os
+build/src/audio/audio_thread.o:    OPTFLAGS := -Os
+
+build/src/libc_sprintf.o: OPTFLAGS := -Ofast
+build/src/libc_math64.o:  OPTFLAGS := -Ofast
 
 build/src/libultra/libc/ldiv.o:    OPTFLAGS := -Os
 build/src/libultra/libc/string.o:  OPTFLAGS := -Os
@@ -355,10 +361,10 @@ build/src/libultra/libc/ll.o:      OPTFLAGS := -O2
 build/src/libultra/libc/ll.o: MIPS_VERSION := -mips3
 
 # cc & asm-processor
-build/src/libultra/gu/sqrtf.o:       OPTFLAGS := -Os
-build/src/libultra/gu/sinf.o:        OPTFLAGS := -Os
+build/src/libultra/gu/sqrtf.o:       OPTFLAGS := -Ofast
+build/src/libultra/gu/sinf.o:        OPTFLAGS := -Ofast
 build/src/libultra/gu/lookat.o:      OPTFLAGS := -Os
-build/src/libultra/gu/ortho.o:       OPTFLAGS := -Os 
+build/src/libultra/gu/ortho.o:       OPTFLAGS := -Os
 build/src/libultra/gu/perspective.o: OPTFLAGS := -Os
 build/src/libultra/gu/mtxutil.o:     OPTFLAGS := -Os
 build/src/libultra/gu/cosf.o:        OPTFLAGS := -Os
diff --git a/include/mods.h b/include/mods.h
index 6930f516..fd93b357 100644
--- a/include/mods.h
+++ b/include/mods.h
@@ -8,17 +8,27 @@
 */
 #define MODS_LEVEL_SELECT 0
 
-
 /**
  * Sound Effects Jukebox:
  * Ability to play sound effects inside the expert sound menu
 */
 #define MODS_SFX_JUKEBOX 0
 
+/**
+ * FPS Counter:
+ * Press L to toggle FPS Display
+*/
+#define MODS_FPS_COUNTER 0
+
+
 /* ************************* */
 
 #if MODS_LEVEL_SELECT == 1
 void Map_LevelSelect(void);
 #endif
 
+#if MODS_FPS_COUNTER == 1
+static void Play_RenderFps(void);
+#endif
+
 #endif
diff --git a/src/audio/audio_general.c b/src/audio/audio_general.c
index ff1247ba..1bea0140 100644
--- a/src/audio/audio_general.c
+++ b/src/audio/audio_general.c
@@ -688,7 +688,6 @@ void Audio_SetSfxProperties(u8 bankId, u8 entryIndex, u8 channelId) {
         sSfxChannelState[channelId].pan = pan;
     }
 }
-
 f32 Audio_UpdateDopplerShift(f32* srcPos, f32* srcVel, f32 soundSpeed, f32* curDopplerShift) {
     f32 xVel;
     f32 zVel;
@@ -704,6 +703,12 @@ f32 Audio_UpdateDopplerShift(f32* srcPos, f32* srcVel, f32 soundSpeed, f32* curD
     f32 targetDopplerShift;
     s32 pad;
 
+#ifdef AVOID_UB
+    if ((srcPos == NULL) || (srcVel == NULL) || (curDopplerShift == NULL)) {
+        return 0.0f;
+    }
+#endif
+
     xPos = srcPos[0];
     zPos = srcPos[2];
     xVel = srcVel[0];
@@ -2215,7 +2220,11 @@ void Audio_UpdateBlueMarineNoise(u8 playerId) {
 void Audio_UpdatePlayerFreqMod(void) {
     u8 playerId;
 
+#ifdef AVOID_UB
+    for (playerId = 0; playerId < gCamCount; playerId++) {
+#else
     for (playerId = 0; playerId < 4; playerId++) {
+#endif
         switch (sPlayerNoise[playerId].form) {
             case FORM_ARWING:
                 Audio_UpdateArwingNoise(playerId);
diff --git a/src/audio/audio_heap.c b/src/audio/audio_heap.c
index 2f59b183..df30ca33 100644
--- a/src/audio/audio_heap.c
+++ b/src/audio/audio_heap.c
@@ -973,7 +973,7 @@ SampleCacheEntry* AudioHeap_AllocPersistentSampleCacheEntry(u32 size) {
 void AudioHeap_DiscardSampleCaches(void) {
     s32 fontId;
     s32 i;
-    s32 numFonts;
+    s32 numFonts = gSoundFontTable->numEntries;
     s32 pad;
     s32 sampleBankId2;
     s32 sampleBankId1;
@@ -983,7 +983,10 @@ void AudioHeap_DiscardSampleCaches(void) {
     Instrument* instrument;
     SampleCacheEntry* entry;
 
-    numFonts = gSoundFontTable->numEntries;
+#ifdef AVOID_UB
+    entry = gPersistentSampleCache.entries;
+#endif
+
     for (fontId = 0; fontId < numFonts; fontId++) {
         sampleBankId1 = gSoundFontList[fontId].sampleBankId1;
         sampleBankId2 = gSoundFontList[fontId].sampleBankId2;
diff --git a/src/engine/fox_display.c b/src/engine/fox_display.c
index 0e1e55d1..4385cd18 100644
--- a/src/engine/fox_display.c
+++ b/src/engine/fox_display.c
@@ -1,3 +1,4 @@
+#include "mods.h"
 #include "global.h"
 #include "assets/ast_arwing.h"
 #include "assets/ast_allies.h"
@@ -1722,4 +1723,11 @@ void Play_Draw(void) {
     func_display_80051B30();
     sPlayersVisible[gPlayerNum] = 0;
     Matrix_Pop(&gGfxMatrix);
+#if MODS_FPS_COUNTER == 1
+    Play_RenderFps();
+#endif
 }
+
+#if MODS_FPS_COUNTER == 1
+#include "../mods/fpscounter.c"
+#endif
diff --git a/src/libultra/gcc_fix/__floatundisf.c b/src/libultra/gcc_fix/__floatundisf.c
new file mode 100644
index 00000000..b69a6103
--- /dev/null
+++ b/src/libultra/gcc_fix/__floatundisf.c
@@ -0,0 +1,27 @@
+#ifdef COMPILER_GCC
+
+typedef union DoubleFloatUnion {
+    double d;
+    long long int ll;
+    unsigned long long ull;
+} DoubleFloatUnion;
+
+/**
+ * Gets float32 from uint64_t.
+ *
+ * https://gcc.gnu.org/onlinedocs/gccint/the-gcc-low-level-runtime-library/routines-for-floating-point-emulation.html#c.__floatundisf
+ */
+float __floatundisf(unsigned long long i) {
+    register DoubleFloatUnion dull;
+    register float ret;
+
+    dull.ull = i;
+    __asm__("cvt.s.l %0, %1" : "=f"(ret) : "f"(dull.d));
+    if ((long) i < 0) {
+        // cvt.s.l assumes signed input, adjust output
+        ret += 4294967296.0f; // 2^32
+    }
+
+    return ret;
+}
+#endif
diff --git a/src/libultra/libc/ll.c b/src/libultra/libc/ll.c
index a3cee6d7..6f64e972 100644
--- a/src/libultra/libc/ll.c
+++ b/src/libultra/libc/ll.c
@@ -1,3 +1,4 @@
+#include "mods.h"
 
 long long __ull_rshift(unsigned long long left, unsigned long long right) {
     return left >> right;
@@ -44,3 +45,10 @@ long long __ll_mod(long long left, long long right) {
 long long __ll_rshift(long long left, long long right) {
     return left >> right;
 }
+
+// IDO FIX
+#if MODS_FPS_COUNTER == 1
+float __ull_to_f(unsigned long long u) {
+    return u;
+}
+#endif
diff --git a/src/mods/fpscounter.c b/src/mods/fpscounter.c
new file mode 100644
index 00000000..2be76dff
--- /dev/null
+++ b/src/mods/fpscounter.c
@@ -0,0 +1,47 @@
+#include "global.h"
+
+// SDK states that 1 cycle takes about 21.33 nanoseconds
+#if 1
+#define SECONDS_PER_CYCLE 0.00000002133f
+#else
+// Use this macro if your N64 CPU is overclocked to 125 Mhz (x2 Multiplier)
+#define SECONDS_PER_CYCLE 0.000000016f
+#endif
+
+#define FPS_COUNTER_X_POS 14
+#define FPS_COUNTER_Y_POS 9
+
+static OSTime gLastOSTime = 0;
+static float gFrameTime = 0.0f;
+static u16 gFrames = 0;
+static u16 gFPS = 0;
+static u8 gRenderFPS = false;
+
+static void CalculateFrameTimeFromOSTime(OSTime diff) {
+    gFrameTime += diff * SECONDS_PER_CYCLE;
+    gFrames++;
+}
+
+static void Play_RenderFps(void) {
+    // Toggle rendering framerate with the L button.
+    if (gControllerPress[0].button & L_TRIG) {
+        gRenderFPS ^= 1;
+    }
+    if (gRenderFPS) {
+        OSTime newTime = osGetTime();
+        CalculateFrameTimeFromOSTime(newTime - gLastOSTime);
+        // If frame time is longer or equal to a second, update FPS counter.
+        if (gFrameTime >= 1.0f) {
+            gFPS = gFrames;
+            gFrames = 0;
+            gFrameTime -= 1.0f;
+        }
+
+        /* Draw */
+        RCP_SetupDL(&gMasterDisp, 0x53);
+        gDPSetPrimColor(gMasterDisp++, 0, 0, 255, 255, 0, 255);
+        Graphics_DisplaySmallText(FPS_COUNTER_X_POS, FPS_COUNTER_Y_POS, 1.0f, 1.0f, "FPS:");
+        Graphics_DisplaySmallNumber(FPS_COUNTER_X_POS + 35, FPS_COUNTER_Y_POS, gFPS);
+        gLastOSTime = newTime;
+    }
+}
diff --git a/src/mods/levelselect.c b/src/mods/levelselect.c
index 55718f5e..5c5f8da6 100644
--- a/src/mods/levelselect.c
+++ b/src/mods/levelselect.c
@@ -3,13 +3,18 @@
 
 extern PlanetId sPlanetList[15];
 extern PlanetId sCurrentPlanetId;
+extern s32 D_menu_801B8280;
+extern s32 D_menu_801CD968;
+
+void Map_801A61B4(LevelId level);
 void Map_801A6368(void);
 void Map_801A914C(void);
+void Map_801A6628(void);
 
 void Map_LevelSelect(void) {
     static char* sLevelSelectPlanetNames[] = {
-        "CORNERIA", "METEO",   "TITANIA",  "SECTOR X", "AQUAS",  "BOLSE",    "VENOM", "FORTUNA",
-        "AREA 6",   "MACBETH", "SECTOR Z", "ZONESS",   "KATINA", "SECTOR Y", "SOLAR",
+        "METEO",  "AREA 6",   "BOLSE",   "SECTOR Z", "SECTOR X", "SECTOR Y", "KATINA", "MACBETH",
+        "ZONESS", "CORNERIA", "TITANIA", "AQUAS",    "FORTUNA",  "VENOM",    "SOLAR",
     };
 
     if (gControllerPress[0].button & L_JPAD) {
@@ -33,10 +38,19 @@ void Map_LevelSelect(void) {
     }
 
     /* Draw */
+    if ((sCurrentPlanetId >= 0) && (sCurrentPlanetId < PLANET_MAX)) {
+        RCP_SetupDL(&gMasterDisp, 0x53);
+        gDPSetPrimColor(gMasterDisp++, 0, 0, 255, 255, 0, 255);
 
-    RCP_SetupDL(&gMasterDisp, 0x53);
-    gDPSetPrimColor(gMasterDisp++, 0, 0, 255, 255, 0, 255);
+        Graphics_DisplaySmallText(20, 200, 1.0f, 1.0f, "PLANET:");
+        Graphics_DisplaySmallText(80, 200, 1.0f, 1.0f, sLevelSelectPlanetNames[sCurrentPlanetId]);
+    }
 
-    Graphics_DisplaySmallText(20, 200, 1.0f, 1.0f, "PLANET:");
-    Graphics_DisplaySmallText(80, 200, 1.0f, 1.0f, sLevelSelectPlanetNames[gCurrentPlanet]);
+    // Bypass briefing
+    if (gControllerPress[0].button & A_BUTTON) {
+        Map_801A61B4(gCurrentLevel);
+        D_menu_801B8280 = 0;
+        D_menu_801CD968 = 0;
+        Map_801A6628();
+    }
 }
diff --git a/src/overlays/ovl_menu/fox_map.c b/src/overlays/ovl_menu/fox_map.c
index f94c7875..4e6a22bc 100644
--- a/src/overlays/ovl_menu/fox_map.c
+++ b/src/overlays/ovl_menu/fox_map.c
@@ -2539,7 +2539,7 @@ void Map_801A1C14(void) {
             D_menu_801CD964 = 1;
             D_menu_801CD96C = 1;
             // clang-format off
-            for (i = 0; i < 15; i++) {D_menu_801CD900[i] = 0;}
+            for (i = 0; i < 15; i++) { D_menu_801CD900[i] = 0; }
             // clang-format on
             D_menu_801CD970 = 0;
 
@@ -2557,7 +2557,7 @@ void Map_801A1C14(void) {
 }
 
 bool Map_801A2304(void) {
-    s32 ret = false;
+    bool ret = false;
     f32 sp28;
     f32 sp24;
     f32 sp20;
diff --git a/yamls/us/main.yaml b/yamls/us/main.yaml
index 98f9b483..c80f1b94 100644
--- a/yamls/us/main.yaml
+++ b/yamls/us/main.yaml
@@ -47,6 +47,9 @@
       - [0x206B0, c, libc_math64]
       - [0x20A60, hasm, libc_math64_fp]
 
+    # GCC
+      - [auto, c, libultra/gcc_fix/__floatundisf]
+      
     # Libultra
       - [0x20BC0, c, libultra/io/controller]
       - [0x20F80, c, libultra/io/contreaddata]